[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-ietf-rohc-tcp-taroc) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 4996

Network Working Group               Ghyslain Pelletier, Editor, Ericsson
INTERNET-DRAFT                               Lars-Erik Jonsson, Ericsson
Expires: August 2005                     Mark A West, Siemens/Roke Manor
                                         Carsten Bormann, TZI/Uni Bremen
                                              Kristofer Sandlund, Effnet
                                                       February 21, 2005


                    RObust Header Compression (ROHC):
                     A Profile for TCP/IP (ROHC-TCP)
                        <draft-ietf-rohc-tcp-09.txt>


Status of this memo

   By submitting this Internet-Draft, I (we) certify that any applicable
   patent or other IPR claims of which I am (we are) aware have been
   disclosed, and any of which I (we) become aware will be disclosed, in
   accordance with RFC 3668 (BCP 79).

   By submitting this Internet-Draft, I (we) accept the provisions of
   Section #3 of RFC 3667 (BCP 78).

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/lid-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This document is a submission of the IETF ROHC WG. Comments should be
   directed to the ROHC WG mailing list, rohc@ietf.org.


Abstract

   This document specifies a ROHC (Robust Header Compression) profile
   for compression of TCP/IP packets. The profile, called ROHC-TCP, is a
   robust header compression scheme for TCP/IP that provides improved
   compression efficiency and enhanced capabilities for compression of
   various header fields including TCP options.




Pelletier, et al.                                               [Page 1]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   Existing TCP/IP header compression schemes do not work well when used
   over links with significant error rates and long round-trip times.
   For many bandwidth-limited links where header compression is
   essential, such characteristics are common. In addition, existing
   schemes (RFC 1144 [14], RFC 2507 [21]) have not addressed how to
   compress TCP options such as SACK (Selective Acknowledgements) (RFC
   2018 [20], RFC 2883 [22]) and Timestamps (RFC 1323 [15]).


Table of Contents

   1. Introduction.....................................................4
   2. Terminology......................................................4
   3. Background.......................................................5
      3.1. Existing TCP/IP Header Compression Schemes..................6
      3.2. Classification of TCP/IP Header Fields......................7
      3.3. Characteristics of Short-lived TCP Transfers................8
   4. Overview of the TCP/IP Profile...................................9
      4.1. General Concepts............................................9
      4.2. Context Replication.........................................9
      4.3. State Machines and Profile Operation........................9
      4.4. Packet Formats and Encoding Methods........................10
      4.5. Irregular Chain............................................10
      4.6. TCP Options................................................10
         4.6.1. Compressing Extension Headers.........................10
   5. Compressor and decompressor State Machines......................10
      5.1. Compressor States and Logic................................11
         5.1.1. Initialization and Refresh (IR) State.................11
         5.1.2. Compression (CO) State................................11
         5.1.3. Feedback Logic........................................12
         5.1.4. State Transition Logic................................12
            5.1.4.1. Optimistic Approach, Upward Transition...........12
            5.1.4.2. Optional Acknowledgements (ACKs), Upward Transition
            ..........................................................12
            5.1.4.3. Timeouts, Downward Transition....................13
            5.1.4.4. Negative ACKs (NACKs), Downward Transition.......13
            5.1.4.5. Need for Updates, Downward Transition............13
         5.1.5. State Machine Supporting Context Replication..........13
      5.2. Decompressor States and Logic..............................14
         5.2.1. No Context (NC) State.................................15
         5.2.2. Static Context (SC) State.............................15
         5.2.3. Full Context (FC) State...............................15
         5.2.4. Allowing Decompression................................16
         5.2.5. Reconstruction and Verification.......................16
         5.2.6. Actions upon CRC Failure..............................16
         5.2.7. Feedback Logic........................................17
   6. ROHC-TCP - TCP/IP Compression (Profile 0x0006)..................18
      6.1. Profile-specific Encoding Methods..........................18
         6.1.1. inferred_mine_header_checksum().......................18
         6.1.2. inferred_ip_v4_header_checksum()......................19
         6.1.3. inferred_ip_v4_length()...............................19



Pelletier, et. al                                               [Page 2]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


         6.1.4. inferred_ip_v6_length()...............................19
         6.1.5. inferred_offset().....................................20
         6.1.6. Scaled TCP Sequence Number Encoding...................20
         6.1.7. Scaled Acknowledgement Number Encoding................21
      6.2. Considerations for the Feedback Channel....................22
      6.3. Control Fields in the ROHC-TCP Context.....................22
         6.3.1. Master Sequence Number (MSN)..........................23
         6.3.2. IP-ID Behavior........................................23
         6.3.3. Explicit Congestion Notification (ECN) in ROHC-TCP....24
      6.4. CRC Calculations...........................................24
      6.5. Initialization.............................................24
   7. Packet Types....................................................25
      7.1. Compressed Header Chains...................................25
      7.2. Compressing TCP Options with List Compression..............26
         7.2.1. List Compression......................................26
         7.2.2. Table-based Item Compression..........................27
         7.2.3. Item Tables...........................................28
         7.2.4. Constraints to List Compression.......................29
         7.2.5. Item Table Mappings...................................29
         7.2.6. Compressed Lists in Dynamic Chain.....................30
         7.2.7. Irregular Chain Items for TCP Options.................30
         7.2.8. Replication of TCP Options............................31
      7.3. Initialization and Refresh Packets (IR)....................31
      7.4. Context Replication Packets (IR-CR)........................33
      7.5. Compressed Packets (CO)....................................34
   8. Packet Formats..................................................35
      8.1. Design rationale for compressed base headers...............35
      8.2. Global Control Fields......................................38
      8.3. General Structures.........................................38
      8.4. Extension Headers..........................................42
         8.4.1. IPv6 DEST opt header..................................42
         8.4.2. IPv6 HOP opt header...................................43
         8.4.3. IPv6 Routing Header...................................43
         8.4.4. GRE Header............................................44
         8.4.5. MINE header...........................................47
         8.4.6. Authentication Header (AH) header.....................48
         8.4.7. Encapsulation Security Payload (ESP) header...........49
      8.5. IP Header..................................................51
         8.5.1. Structures Common for IPv4 and IPv6...................51
         8.5.2. IPv6 Header...........................................51
         8.5.3. IPv4 Header...........................................54
      8.6. TCP Header.................................................58
      8.7. TCP Options................................................64
      8.8. Structures used in Compressed Base Headers.................74
      8.9. Feedback Formats and Options...............................89
         8.9.1. Feedback Formats......................................89
         8.9.2. Feedback Options......................................90
            8.9.2.1. The CRC option...................................90
            8.9.2.2. The REJECT option................................90
            8.9.2.3. The MSN-NOT-VALID option.........................91
            8.9.2.4. The MSN option...................................91



Pelletier, et. al                                               [Page 3]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


            8.9.2.5. The LOSS option..................................91
            8.9.2.6. Unknown option types.............................91
            8.9.2.7. The CONTEXT_MEMORY Feedback Option...............92
   9. Security Consideration..........................................92
   10. IANA Considerations............................................93
   11. Acknowledgments................................................93
   12. Authors' Addresses.............................................93
   13. References.....................................................94
      13.1. Normative references......................................94
      13.2. Informative References....................................95


1.  Introduction

   There are several reasons to perform header compression on low- or
   medium-speed links for TCP/IP traffic, and these have already been
   discussed in RFC 2507 [21]. Additional considerations that make
   robustness an important objective for a TCP compression scheme are
   introduced in [10]. Finally, existing TCP/IP header compression
   schemes (RFC 1144 [14], RFC 2507 [21]) are limited in their handling
   of the TCP options field and cannot compress the headers of
   handshaking packets (SYNs and FINs).

   It is thus desirable for a header compression scheme to be able to
   handle loss on the link between the compression and decompression
   point as well as loss before the compression point. The header
   compression scheme also needs to consider how to efficiently compress
   short-lived TCP transfers and TCP options, such as SACK (RFC 2018
   [20], RFC 2883 [22]) and Timestamps (RFC 1323 [15]).

   The ROHC WG has developed a header compression framework on top of
   which various profiles can be defined for different protocol sets, or
   for different compression strategies. This document defines a TCP/IP
   compression profile for the ROHC framework [2], compliant with the
   requirements on ROHC TCP/IP header compression [10].

   Specifically, it describes a header compression scheme for TCP/IP
   header compression (ROHC-TCP) that is robust against packet loss and
   that offers enhanced capabilities, in particular for the compression
   of header fields including TCP options. The profile identifier for
   TCP/IP compression is 0x0006.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD, "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

   This document reuses some of the terminology found in RFC 3095 [2].
   In addition, this document uses or defines the following terms:



Pelletier, et. al                                               [Page 4]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   Base context

     The base context is a context that has been validated by both the
     compressor and the decompressor. A base context can be used as the
     reference when building a new context using replication.

   Base CID

     The Base Context Identifier is the CID used to identify the Base
     Context, where information needed for context replication can
     be extracted from.

   Context replication

     Context replication is the mechanism that establishes and
     initializes a new context based on another existing valid context
     (a base context). This mechanism is introduced to reduce the
     overhead of the context establishment procedure, and is especially
     useful for compression of multiple short-lived TCP connections that
     may be occurring simultaneously or near-simultaneously.

   ROHC Context Replication (ROHC-CR)

     "ROHC-CR" in this document normatively refers to the context
     replication mechanism for ROHC profiles defined in [3].

   ROHC Formal Notation (ROHC-FN)

     "ROHC-FN" in this document normatively refers to the formal
     notation for ROHC profiles defined in [4], including the library of
     encoding methods it specifies.

   Short-lived TCP Transfer

     Short-lived TCP transfers refer to TCP connections transmitting
     only small amounts of data for each single connection. Short TCP
     flows seldom need to operate beyond the slow-start phase of TCP to
     complete their transfer, which also means that the transmission
     ends before any significant increase of the TCP congestion window
     may occur.


3.  Background

   This chapter provides some background information on TCP/IP header
   compression.  The fundamentals of general header compression may be
   found in [2]. In the following sections, two existing TCP/IP header
   compression schemes are first described along with a discussion of
   their limitations, followed by the classification of TCP/IP header
   fields. Finally, some of the characteristics of short-lived TCP
   transfers are summarized.



Pelletier, et. al                                               [Page 5]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   The behavior analysis of TCP/IP header fields among multiple short-
   lived connections may be found in [11].


3.1.  Existing TCP/IP Header Compression Schemes

   Compressed TCP (CTCP) and IP Header Compression (IPHC) are two
   different schemes that may be used to compress TCP/IP headers. Both
   schemes transmit only the differences from the previous header in
   order to reduce the large overhead of the TCP/IP header.

   The CTCP (RFC 1144 [14]) compressor detects transport-level
   retransmissions and sends a header that updates the context
   completely when they occur. While CTCP works well over reliable
   links, it is vulnerable when used over less reliable links as even a
   single packet loss results in loss of synchronization between the
   compressor and the decompressor. This in turn leads to the TCP
   receiver discarding all remaining packets in the current window
   because of a checksum error. This effectively prevents the TCP Fast
   Retransmit algorithm (RFC 2001) from being triggered. In such case,
   the compressor must wait until the TCP timeout to resynchronize.

   To reduce the errors due to the inconsistent contexts between
   compressor and decompressor when compressing TCP, IPHC (RFC 2507
   [21]) improves somewhat on CTCP by augmenting the repair mechanism of
   CTCP with a local repair mechanism called TWICE and with a link-level
   nacking mechanism to request a header that updates the context.

   The TWICE algorithm assumes that only the Sequence Number field of
   TCP segments are changing with the deltas between consecutive packets
   being constant in most cases. This assumption is however not always
   true, especially when TCP Timestamps and SACK options are used.

   The full header request mechanism requires a feedback channel that
   may be unavailable in some circumstances. This channel is used to
   explicitly request that the next packet be sent with an uncompressed
   header to allow resynchronization without waiting for a TCP timeout.
   In addition, this mechanism does not perform well on links with long
   round-trip time.

   Both CTCP and IPHC are also limited in their handling of the TCP
   options field. For IPHC, any change in the options field (caused by
   timestamps or SACK, for example) renders the entire field
   uncompressible, while for CTCP such a change in the options field
   effectively disables TCP/IP header compression altogether.

   Finally, existing TCP/IP compression schemes do not compress the
   headers of handshaking packets (SYNs and FINs). Compressing these
   packets may greatly improve the overall header compression ratio for
   the cases where many short-lived TCP connections share the same link.




Pelletier, et. al                                               [Page 6]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


3.2.  Classification of TCP/IP Header Fields

   Header compression is possible due to the fact that there is much
   redundancy between header field values within packets, especially
   between consecutive packets. To utilize these properties for TCP/IP
   header compression, it is important to understand the change patterns
   of the various header fields.

   All fields of the TCP/IP packet header have been classified in detail
   in [11]. The main conclusion is that most of the header fields can
   easily be compressed away since they never or seldom change. The
   following fields do however require more sophisticated mechanisms:

       - IPv4 Identification (16 bits)         - IP-ID
       - TCP Sequence Number (32 bits)         - SN
       - TCP Acknowledgement Number (32 bits)  - ACKN
       - TCP Reserved (4 bits)
       - TCP ECN flags (2 bits)                - ECN
       - TCP Window (16 bits)                  - WINDOW
       - TCP Options
          - Maximum Segment Size (4 octets)    - MSS
          - Window Scale (3 octets)            - WSopt
          - SACK Permitted (2 octets)
          - TCP SACK                           - SACK
          - TCP Timestamp (32 bits)            - TS

   The assignment of IP-ID values can be done in various ways, which are
   Sequential, Sequential jump, Random or constant to a value of zero.
   However, designers of IPv4 stacks for cellular terminals should use
   an assignment policy close to Sequential.  Some IPv4 stacks do use a
   sequential assignment when generating IP-ID values but do not
   transmit the contents this field in network byte order; instead it is
   sent with the two octets reversed.  In this case, the compressor can
   compress the IP-ID field after swapping the bytes. Consequently, the
   decompressor also swaps the bytes of the IP-ID after decompression to
   regenerate the original IP-ID.  In RFC 3095 [2], the IP-ID is
   generally inferred from the RTP Sequence Number. However, with
   respect to TCP compression, the analysis in [11] reveals that there
   is no obvious candidate to this purpose among the TCP fields.

   The change pattern of several TCP fields (Sequence Number,
   Acknowledgement Number, Window, etc.) is very hard to predict and
   differs entirely from the behavior of RTP fields discussed in [2]. Of
   particular importance to a TCP/IP header compression scheme is the
   understanding of the sequence and acknowledgement number [11].

   Specifically, the sequence number can be anywhere within a range
   defined by the TCP window at any point on the path (i.e. wherever a
   compressor might be deployed). Missing packets or retransmissions can
   cause the TCP sequence number to fluctuate within the limits of this




Pelletier, et. al                                               [Page 7]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   window. The TCP window also bound the jumps in acknowledgement
   number.

   Another important behavior of the TCP/IP header is the dependency
   between the sequence number and the acknowledgment number. It is well
   known that most TCP connections only have one-way traffic (web
   browsing and FTP downloading, for example). This means that on the
   forward path (from server to client), only the sequence number is
   changing while the acknowledgement number remains constant for most
   packets; on the backward path (from client to server), only the
   sequence number is changing and the acknowledgement number remains
   constant for most packets.

   With respect to TCP options, it is noted that most options (such as
   MSS, WSopt, SACK-permitted, etc.) may appear only on a SYN segment.
   Every implementation should (and we expect most will) ignore unknown
   options on SYN segments.

   Headers specific to Mobile IP (for IPv4 or IPv6) do not receive any
   special treatment in this document, for reasons similar as those
   described in [2].


3.3.  Characteristics of Short-lived TCP Transfers

   Recent studies shows that the majority of TCP flows are short-lived
   transfers with an average and a median size no larger than 10KB.
   Short-lived TCP transfers will degrade the performance of header
   compression schemes that establish a new context by initially sending
   full headers.

   It is hard to improve the performance for a single, unpredictable,
   short-lived connection. However, there are common cases where there
   will be multiple TCP connections between the same pair of hosts. A
   mobile user browsing several web pages from the same web server (this
   is more the case with HTTP/1.0 than HTTP/1.1) is one example.

   In such case, multiple short-lived TCP/IP flows occur simultaneously
   or near simultaneously within a relatively short time interval. It
   may be expected that most (if not all) of the IP header of the these
   connections will be almost identical to each other, with only small
   relative jumps for the IP-ID field.

   Furthermore, a subset of the TCP fields may also be very similar from
   one connection to another. For example, one of the port numbers may
   be reused (the service port) while the other (the ephemeral port) may
   be changed only by a small amount relative to the just-closed
   connection.

   With regard to header compression, this means that parts of a
   compression context used for a TCP connection may be reusable for



Pelletier, et. al                                               [Page 8]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   another TCP connection. A mechanism supporting context replication,
   where a new context is initialized from an existing one, provide
   useful optimizations for a sequence of short-lived TCP connections.

   Context replication is possible due to the fact that there is much
   similarity in header field values and context values among multiple
   simultaneous or near simultaneous connections. All header fields and
   related context values have been classified in detail in [11]. The
   main conclusion is that most part of the IP sub-context, some TCP
   fields, and some context values can easily be replicated since they
   seldom change or change with only a small jump.


4.  Overview of the TCP/IP Profile


4.1.  General Concepts

   Many of the concepts behind the ROHC-TCP profile are similar to those
   described in RFC 3095 [2]. Like for other ROHC profiles, ROHC-TCP
   makes use of the ROHC protocol as described in [2], in sections 5.1
   to 5.2.6. This includes data structures, reserved packet types,
   general packet formats, segmentation and initial decompressor
   processing.


4.2.  Context Replication

   For ROHC-TCP, context replication may be particularly useful for
   short-lived TCP flows [10]. ROHC-TCP therefore supports context
   replication as defined in ROHC-CR [3]; the compressor MAY support
   context replication, while a decompressor implementation is REQUIRED
   to support decompression of the IR-CR packet type.


4.3.  State Machines and Profile Operation

   Header compression with ROHC can be characterized as an interaction
   between two state machines, one compressor machine and one
   decompressor machine, each instantiated once per context.

   For ROHC-TCP compression, the compressor has two states and the
   decompressor has three states. The two compressor states are the
   Initialization and Refresh (IR) state, and the Compression (CO)
   state. The three states of the decompressor are No Context (NC),
   Static Context (SC) and Full Context (FC). The compressor may also
   implement a third state, the Context Replication (CR) state, to
   support context replication ROHC-CR [3]. Transitions need not be
   synchronized between the two state machines.





Pelletier, et. al                                               [Page 9]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


4.4.  Packet Formats and Encoding Methods

   The packet formats used for ROHC-TCP and found in this document are
   defined using the formal notation, ROHC-FN. The formal notation is
   used to provide an unambiguous representation of the packet formats
   and a clear definition of the encoding methods. The encoding methods
   used in the packet formats for ROHC-TCP are defined in [4].


4.5.  Irregular Chain

   The ROHC-TCP profile defines an irregular chain for each header type,
   in addition to the static and dynamic chains as used in RFC 3095 [2].

   The irregular chain handles fields for which no predictable change
   pattern could be identified, i.e. fields from the TCP, IP and
   extension headers that have an irregular behavior and therefore have
   to be included in each compressed packet. This chain is attached to
   compressed packet in order to make it possible to carry arbitrary
   combinations of headers.


4.6.  TCP Options

   The list compression scheme in ROHC-TCP is a downscaled version of
   the list compression in [2], allowing option content to be
   established so that TCP options can be added or removed from the
   packet without having to send the entire option uncompressed.


4.6.1.  Compressing Extension Headers

   In RFC 3095 [2], list compression is used to compress extension
   headers. ROHC-TCP compresses the same type of extension headers as in
   [2]. However, these headers are treated exactly as other headers and
   thus have a static chain, a dynamic chain, an irregular chain and a
   replicate chain.

   The consequence is that headers appearing in or disappearing from the
   flow being compressed will lead to changes to the static chain.
   However, the change pattern of extension headers is not deemed to
   impair compression efficiency with respect to this design strategy.


5.  Compressor and decompressor State Machines

   The header compression state machines and their associated logic as
   specified in this section are a simplified version of the ones found
   in [2].





Pelletier, et. al                                              [Page 10]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


5.1.  Compressor States and Logic

   The two compressor states are the Initialization and Refresh (IR)
   state, and the Compression (CO) state. The compressor always starts
   in the lower compression state (IR). The compressor will normally
   operate in the higher compression state (CO), under the constraint
   that the compressor is sufficiently confident that the decompressor
   has the information necessary to reconstruct a header compressed
   according to this state.

   The figure below shows the state machine for the compressor. The
   details of each state, state transitions, and compression logic are
   given in sub-sections following the figure.

                 Optimistic approach / ACK     ACK
               +------>------>------>------+  +->-+
               |                           |  |   |
               |                           v  |   v
           +----------+                  +----------+
           | IR State |                  | CO State |
           +----------+                  +----------+
               ^                                |
               |  Timeout / NACK / STATIC-NACK  |
               +-------<-------<-------<--------+

   The transition from IR state to CO state is based on the following
   principles: the need for update and the optimistic approach principle
   or, if a feedback channel is established, feedback received from the
   decompressor.


5.1.1.  Initialization and Refresh (IR) State

   The purpose of the IR state is to initialize the static parts of the
   context at the decompressor or to recover after failure. In this
   state, the compressor sends complete header information. This
   includes static and non-static fields in uncompressed form plus some
   additional information.

   The compressor stays in the IR state until it is fairly confident
   that the decompressor has received the static information correctly.


5.1.2.  Compression (CO) State

   The purpose of the CO state is to efficiently communicate
   irregularities in the packet stream when needed while maintaining the
   most optimal compression ratio. When operating in this state, the
   compressor normally sends most or all of the information in a
   compressed form.




Pelletier, et. al                                              [Page 11]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


5.1.3.  Feedback Logic

   The compressor state machine makes use of feedback from decompressor
   to compressor for transitions in the backward direction, and
   optionally to improve the forward transition.

   The reception of either positive feedback (ACKs) or negative feedback
   (NACKs) establishes the feedback channel from the decompressor. Once
   there is an established feedback channel, the compressor makes use of
   this feedback for optionally improving the transitions among
   different states. This helps increasing the compression efficiency by
   providing the information needed for the compressor to achieve the
   necessary confidence level. When the feedback channel is established,
   it becomes superfluous for the compressor to send periodic refreshes.


5.1.4.  State Transition Logic

   The compressor makes its decisions about when to transit between the
   IR and the CO states on the basis of:

      - variations in the packet headers
      - positive feedback from decompressor (Acknowledgements -- ACKs)
      - negative feedback from decompressor (Negative ACKS -- NACKs)
      - confidence level regarding error-free decompression of a packet


5.1.4.1.  Optimistic Approach, Upward Transition

   Transition to the CO state is carried out according to the optimistic
   approach principle. This means that the compressor transits to the CO
   state when it is fairly confident that the decompressor has received
   enough information to correctly decompress packets sent according to
   the higher compression state.

   In general, there are many approaches where the compressor can obtain
   such information. A simple and general approach can be achieved by
   sending uncompressed or partial full headers periodically.


5.1.4.2.  Optional Acknowledgements (ACKs), Upward Transition

   The compressor can also transit to the CO state based on feedback
   received by the decompressor. If a feedback channel is available, the
   decompressor MAY use positive feedback (ACKs) to acknowledge
   successful decompression of packets. Upon reception of an ACK for a
   context-updating packet, the compressor knows that the decompressor
   has received the acknowledged packet and the transition to the CO
   state can be carried out immediately.





Pelletier, et. al                                              [Page 12]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   This functionality is optional, so a compressor MUST NOT expect to
   get such ACKs initially or during normal operation, even if a
   feedback channel is available or established.


5.1.4.3.  Timeouts, Downward Transition

   When the optimistic approach is used (i.e. until a feedback channel
   is established), there will always be a possibility of failure since
   the decompressor may not have received sufficient information for
   correct decompression. Therefore, unless the decompressor has
   established a feedback channel, the compressor MUST periodically
   transit to the IR state.


5.1.4.4.  Negative ACKs (NACKs), Downward Transition

   Negative acknowledgments (NACKs) are also called context requests.
   Upon reception of a NACK, the compressor transits back to the IR
   state and sends updates (such as IR-DYN or IR) to the decompressor.


5.1.4.5.  Need for Updates, Downward Transition

   When the header to be compressed does not conform to the established
   pattern or when the compressor is not confident whether the
   decompressor has the synchronized context, the compressor will
   transit to the IR state.


5.1.5.  State Machine Supporting Context Replication

   For a profile supporting context replication, the additional
   compressor logic (including corresponding state transition and
   feedback logic) defined by ROHC-CR [3] must be added to the
   compressor state machine described above.


















Pelletier, et. al                                              [Page 13]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   The following figure shows the resulting state machine:


                       Optimistic approach / ACK
          +--->------>------>------>------>------>------>---+
          |                                                 |
          |     BCID Selection    Optimistic approach / ACK |  ACK
          | +------>----->------+ +----->----->----->-----+ | +->-+
          | |                   | |                       | | |   |
          | |                   v |                       v v |   v
      +---------+           +---------+                  +---------+
      |   IR    |           |   CR    |                  |   CO    |
      |  State  |           |  State  |                  |  State  |
      +---------+           +---------+                  +---------+
          ^ ^                    |                           |
          | | NACK / STATIC-NACK |                           |
          | +---<-----<-----<----+                           |
          |                                                  |
          |           Timeout / NACK / STATIC-NACK           |
          +-----<-------<-------<-------<-------<-------<----+


5.2.  Decompressor States and Logic

   The three states of the decompressor are No Context (NC), Static
   Context (SC) and Full Context (FC). The decompressor starts in its
   lowest compression state, the NC state. Successful decompression will
   always move the decompressor to the FC state. The decompressor state
   machine normally never leaves the FC state once it has entered this
   state; only repeated decompression failures will force the
   decompressor to transit downwards to a lower state.

   Below is the state machine for the decompressor. Details of the
   transitions between states and decompression logic are given in the
   sub-sections following the figure.


                                 Success
                +-->------>------>------>------>------>--+
                |                                        |
    No Static   |            No Dynamic        Success   |    Success
     +-->--+    |             +-->--+      +--->----->---+    +-->--+
     |     |    |             |     |      |             |    |     |
     |     v    |             |     v      |             v    |     v
   +-----------------+   +---------------------+   +-------------------+
   | No Context (NC) |   | Static Context (SC) |   | Full Context (FC) |
   +-----------------+   +---------------------+   +-------------------+
      ^                         |        ^                         |
      | k_2 out of n_2 failures |        | k_1 out of n_1 failures |
      +-----<------<------<-----+        +-----<------<------<-----+




Pelletier, et. al                                              [Page 14]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


5.2.1.  No Context (NC) State

   Initially, while working in the NC state, the decompressor has not
   yet successfully decompressed a packet.

   Upon receiving an IR or an IR-DYN packet, the decompressor will
   verify the correctness of this packet by validating its header using
   the CRC check. If the decompressed packet is successfully verified,
   the decompressor will update the context and use this packet as the
   reference packet. Once a packet has been decompressed correctly, the
   decompressor can transit to the FC state, and only upon repeated
   failures will it transit back to a lower state.


5.2.2.  Static Context (SC) State

   In the SC state, the decompressor assumes static context damage when
   the CRC check of k_2 out of the last n_2 decompressed packets have
   failed. The decompressor moves to the NC state and discards all
   packets until a packet (e.g. IR or IR-DYN packet) that successfully
   passes the verification check is received. The decompressor may send
   feedback (see section 5.2.7) when assuming static context damage.

   Note that appropriate values for k and n, are related to the residual
   error rate of the link.  When the residual error rate is close to
   zero, k = n = 1 may be appropriate.


5.2.3.  Full Context (FC) State

   In the FC state, the decompressor assumes context damage when the CRC
   check of k_1 out of the last n_1 decompressed packets have failed,
   (where k and n are related to the residual error rate of the link as
   in section 5.2.2). The decompressor moves to the SC state and
   discards all packets until a packet carrying a 7- or 8-bit CRC that
   successfully passes the verification check is received. The
   decompressor may send feedback (see section 5.2.7) when assuming
   context damage.

   Upon receiving an IR or an IR-DYN packet, the decompressor MUST
   verify the correctness of its header using CRC validation. If the
   verification succeeds, the decompressor will update the context and
   use this packet as the reference packet. Consequently, the
   decompressor will convert the packet into the original packet and
   pass it to the network layer of the system.

   Upon receiving other types of packet, the decompressor will
   decompress it. The decompressor MUST verify the correctness of the
   decompressed packet by CRC check. If this verification succeeds, the
   decompressor passes the decompressed packet to the system's network




Pelletier, et. al                                              [Page 15]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   layer. The decompressor will then use this packet as the reference
   value.

   If the received packet is older than the current reference packet
   (based on sequence numbers in the compressed packet or in the
   uncompressed header), the decompressor MAY refrain from using this
   packet as the new reference value, even if the correctness of its
   header was successfully verified.


5.2.4.  Allowing Decompression

   In the No Context state, only packets carrying sufficient information
   on the static fields (i.e. IR packets) can be decompressed.

   In the Static Context state, only packets carrying a 7- or 8-bit CRC
   may be decompressed (i.e. IR, IR-DYN and some CO packets).

   In the Full Context state, decompression may be attempted regardless
   of the type of packet received.

   If decompression may not be performed, the packet is discarded.

   As per ROHC-CR [3], IR-CR packets may be decompressed in any state.


5.2.5.  Reconstruction and Verification

   The CRC carried within compressed headers MUST be used to verify
   decompression. When the decompression is verified and successful, the
   decompressor updates the context with the information received in the
   current header; otherwise if the reconstructed header fails the CRC
   check, these updates MUST NOT be performed.


5.2.6.  Actions upon CRC Failure

   When a CRC check fails, the decompressor MUST discard the packet. The
   actions to be taken when CRC verification fails following the
   decompression of an IR-CR packet are specified in [3]. For other
   packet types carrying a CRC, if feedback is used the logic specified
   in section 5.2.7 must be followed when CRC verification fails.

   Note: Decompressor implementations may attempt corrective or repair
   measures prior to performing the above actions, and the result of any
   attempt MUST be verified using the CRC check.








Pelletier, et. al                                              [Page 16]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


5.2.7.  Feedback Logic

   The decompressor may send positive feedback (ACKs) to initially
   establish the feedback channel for a particular flow. Either positive
   feedback (ACKs) or negative feedback (NACKs) will establish this
   channel. The decompressor will then use the feedback channel to send
   error recovery requests and (optionally) acknowledgements of
   significant context updates.

   Once the decompressor establishes a feedback channel, the compressor
   will operate using an optimistic logic. In particular, this means
   that the compressor will rely on specific decompressor feedback
   logic:

      - the decompressor will send negative acknowledgements in case
        when context damage is assumed or in other failure situations;

      - the decompressor is not strictly expected to send feedback upon
        successful decompression, other than for the purpose of
        improving the forward state transition.

   Once the feedback channel is established, the decompressor is
   REQUIRED to continue sending feedback (subject to the feedback rate
   limiting considerations later in this section) for the lifetime of
   the packet stream as follow:

     In NC state:

        The decompressor SHOULD send a STATIC-NACK if a packet of a type
        other than IR is received, or if an IR packet has failed the CRC
        check.

     In SC state:

        The decompressor SHOULD send a STATIC-NACK when decompression of
        an IR, an IR-DYN or a CO packet carrying a 7-bit CRC fails and
        if static context damage is assumed (see also section 5.2.2).
        If any other packet type is received, the decompressor SHOULD
        treat it as a CRC mismatch when deciding if feedback is to be
        sent.

     In FC state:

        The decompressor SHOULD send a NACK when decompression of any
        packet type fails and if context damage is assumed (see also
        section 5.2.3).

   When decompression fails, the feedback rate SHOULD be limited. For
   example, feedback could be sent only when decompression of several
   consecutive packets have failed. In addition, the decompressor should
   also limit the rate at which feedback is sent on successful



Pelletier, et. al                                              [Page 17]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   decompression, if sent at all. The decompressor may limit the
   feedback rate by sending feedback for one out of a number of packets
   providing the same type of feedback.

   The decompressor MAY optionally send ACKs upon successful
   decompression of any packet type. In particular, when an IR, an IR-
   DYN or any CO packet carrying a 7- or 8-bit CRC is correctly
   decompressed, the compressor may optionally send an ACK.

   Finally, when the decompressor ACKs an IR packet, it MUST use the CRC
   option (see [2], section 5.7.6.3) when sending this feedback. This is
   necessary to ensure that a context does not erroneously become a
   candidate for later use as a base context for replication [3].


6.  ROHC-TCP - TCP/IP Compression (Profile 0x0006)

   This section describes a ROHC profile for TCP/IP compression. The
   profile identifier for ROHC-TCP is 0x0006.


6.1. Profile-specific Encoding Methods

   This section defines encoding methods that are specific to this
   profile. These methods are used in the formal definition of the
   packet formats in section 8.


6.1.1.  inferred_mine_header_checksum()

   This encoding method compresses the minimal encapsulation header
   checksum. This checksum is defined in RFC 2004 [25] as follow:

      Header Checksum

        The 16-bit one's complement of the one's complement sum of all
        16-bit words in the minimal forwarding header.  For purposes of
        computing the checksum, the value of the checksum field is 0.
        The IP header and IP payload (after the minimal forwarding
        header) are not included in this checksum computation.

   The "inferred_mine_header_checksum()" encoding method compresses the
   minimal encapsulation header checksum down to a size of zero bit,
   i.e. no bits are transmitted in compressed headers for this field.
   Using this encoding method, the decompressor infers the value of this
   field using the above computation.








Pelletier, et. al                                              [Page 18]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


6.1.2. inferred_ip_v4_header_checksum()

   This encoding method compresses the header checksum field of the IPv4
   header. This checksum is defined in RFC 791 [5] as follows:

      Header Checksum:  16 bits

        A checksum on the header only.  Since some header fields change
        (e.g., time to live), this is recomputed and verified at each
        point that the internet header is processed.


      The checksum algorithm is:

        The checksum field is the 16 bit one's complement of the one's
        complement sum of all 16 bit words in the header.  For purposes
        of computing the checksum, the value of the checksum field is
        zero.

   The "inferred_ip_v4_header_checksum()" encoding method compresses the
   IPv4 header checksum down to a size of zero bit, i.e. no bits are
   transmitted in compressed headers for this field. Using this encoding
   method, the decompressor infers the value of this field using the
   above computation.


6.1.3.  inferred_ip_v4_length()

   This encoding method compresses the total length field of the IPv4
   header. The total length field of the IPv4 header is defined in RFC
   791 [5] as follows:

      Total Length:  16 bits

        Total Length is the length of the datagram, measured in octets,
        including internet header and data.  This field allows the
        length of a datagram to be up to 65,535 octets.

   The "inferred_ip_v4_length()" encoding method compresses the IPv4
   header checksum down to a size of zero bit, i.e. no bits are
   transmitted in compressed headers for this field. Using this encoding
   method, the decompressor infers the value of this field by counting
   in octets the length of the entire packet after decompression.


6.1.4.  inferred_ip_v6_length()

   This encoding method compresses the payload length field in the IPv6
   header. This length field is defined in RFC 2460 [9] as follow:

      Payload Length:  16-bit unsigned integer



Pelletier, et. al                                              [Page 19]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


        Length of the IPv6 payload, i.e., the rest of the packet
        following this IPv6 header, in octets.  (Note that any extension
        headers present are considered part of the payload, i.e.,
        included in the length count.)

   The "inferred_ip_v6_length()" encoding method compresses the payload
   length field of the IPv6 header down to a size of zero bit, i.e. no
   bits are transmitted in compressed headers for this field. Using this
   encoding method, the decompressor infers the value of this field by
   counting in octets the length of the entire packet after
   decompression.


6.1.5.  inferred_offset()

   This encoding method compresses

   The inferred_offset encoding method is used on the data offset field
   of the TCP header. This field is defined in RFC 793 as:

      Data Offset:  4 bits

        The number of 32 bit words in the TCP Header.  This indicates
        where the data begins.  The TCP header (even one including
        options) is an integral number of 32 bits long.

   The "inferred_offset()" encoding method compresses the data offset
   field of the TCP header down to a size of zero bit, i.e. no bits are
   transmitted in compressed headers for this field. Using this encoding
   method, the decompressor infers the value of this field by first
   decompressing the TCP options list, and by then setting data offset =
   (options length / 4) + 5.


6.1.6.  Scaled TCP Sequence Number Encoding

   On some TCP streams, such as data transfers, the payload size will be
   constants over periods of time. For such streams, the TCP sequence
   number is bound to increase by multiples of the payload size between
   packets. ROHC-TCP provides a method to use scaled compression of the
   TCP sequence number to improve compression efficiency in such case.

   When scaling the TCP sequence number, the residue is the sequence
   number offset from a multiple of the payload size. The precondition
   for the compressor to start using this type of encoding is that the
   compressor must be confident that the decompressor has received a
   number of packets sufficient to establish the value of the residue of
   the scaling function.

   This confidence can be established by sending a number of packets
   that are compressed using an unscaled representation of the sequence



Pelletier, et. al                                              [Page 20]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   numbers, when the payload size is constant. The compressor can then
   start using the scaled sequence number encoding, where the sequence
   number is first downscaled by the value of the payload size and then
   LSB encoded.

   Packets incoming to the compressor for which the value of the residue
   is different than the one that has previously been established MUST
   be sent in a compressed packet that carry the sequence number
   compressed using its unscaled representation, until a stable residue
   value can once again be established at the decompressor.

   Note that when the sequence number wraps around, the value of the
   residue of the scaling function is likely to change, even when the
   payload size remains constant. When this occurs, the compressor MUST
   reestablish the new residue value using the unscaled representation
   of the sequence number as described above.

   Note also that the scaling function applied to the TCP sequence
   number does not use an explicit scaling factor, such as the TS_STRIDE
   used in RFC 3095 [2]. Instead, the payload size is used as the
   scaling factor; as this value can be inferred from the length of the
   packet, there is no need to transmit this field explicitly.

   The expressions for compressing and decompressing the scaled sequence
   number are specified in the definitions of the packet format.


6.1.7. Scaled Acknowledgement Number Encoding

   Similar to the pattern exhibited by sequence numbers, the expected
   increase in the TCP Acknowledgment number will often be a multiple of
   the packet size. For the Sequence Number, the compression scheme can
   use the payload size of the packets as a scaling factor (see section
   6.1.6 above).

   For the Acknowledgement Number, the scaling factor depends on the
   size of packets flowing in the opposite direction; this information
   might not be available to the compressor/decompressor pair. For this
   reason, ROHC-TCP uses an explicit scaling factor to compress the TCP
   Acknowledgement Number.

   For the compressor to use the scaled acknowledgement number encoding,
   it MUST first explicitly transmit the value of the scaling factor
   (ack_stride) to the decompressor, using one of the packet types that
   can carry this information. Once the value of the scaling factor is
   established, before using this scaled encoding the compressor must
   have enough confidence that the decompressor has successfully
   calculated the residue of the scaling function for the
   acknowledgement number. This is done the same way as for the scaled
   sequence number encoding (see section 6.1.6 above).




Pelletier, et. al                                              [Page 21]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   Once the compressor has gained enough confidence that both the value
   of the scaling factor and the value of the residue have been
   established in the decompressor, the compressor can start compress
   packets using the scaled representation of the Acknowledgement
   Number. The compressor MUST NOT use the scaled acknowledgement number
   encoding with the value of the scaling factor (ack_stride) set to
   zero.

   The compressor MAY use the scaled acknowledgement number encoding;
   what value it will use as the scaling factor is up to the compressor
   implementation. In the case where there is a co-located decompressor
   processing packets of the same TCP flow in the opposite direction,
   the scaling factor for the acknowledgement numbers can be set to the
   same value as the scaling factor of the sequence numbers used for
   that flow.


6.2.  Considerations for the Feedback Channel

   The ROHC-TCP profile may be used in environments with or without
   feedback capabilities from decompressor to compressor. ROHC-TCP
   however assumes that if a ROHC feedback channel is available and is
   used at least once by the decompressor, this channel will be present
   during the entire compression operation. Otherwise, if the connection
   is broken and the channel disappears, header compression should be
   restarted.

   To parallel RFC 3095 [2], this is similar to allowing only one mode
   transition per compressor: from the initial unidirectional mode to
   the bi-directional mode of operation, with the transition being
   triggered by the reception of the first packet containing feedback
   from the decompressor. This effectively means that ROHC-TCP does not
   explicitly define any operational modes.


6.3. Control Fields in the ROHC-TCP Context

   A control field is a field that is transmitted from the compressor to
   the decompressor, but is not part of the uncompressed header. Values
   for control fields can be set up in the context of both the
   compressor and the decompressor.

   In ROHC-TCP, a number of control fields are used by the decompressor
   in its interpretation of the packet formats for packets received from
   the compressor. These control fields are not a part of the
   uncompressed header, but are explicitly transmitted inside ROHC-TCP
   packets. Once established at the decompressor, the values of these
   fields should be kept until updated by another packet.






Pelletier, et. al                                              [Page 22]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


6.3.1. Master Sequence Number (MSN)

   Feedback packets of types ACK and NACK carry information about
   sequence number or acknowledgement number from decompressor to
   compressor. Unfortunately, there is no guarantee that sequence number
   and acknowledgement number fields will be used by every IP protocol
   stack. In addition, the combined size of the sequence number field
   and the acknowledgement number field is rather large, and they can
   therefore not be carried efficiently within the feedback packet.

   To overcome this problem, ROHC-TCP introduces a control field called
   the Master Sequence Number (MSN) field. The MSN field is created at
   the compressor, rather than using one of the fields already present
   in the uncompressed header. The compressor increments the value of
   the MSN by one for each packet that it sends.

   The MSN field has the following two functions:

      1. Differentiating between packets when sending feedback data.

      2. Inferring the value of incrementing fields such as the IP-ID.

   The MSN field is present in every packets sent by the compressor. The
   MSN is LSB encoded within the CO packets, and the 16-bit MSN is sent
   in full in IR/IR-DYN packets. The decompressor always sends the MSN
   as part of the feedback information. The compressor can later use the
   MSN to infer which packet the decompressor is acknowledging.

   When the MSN is initialized, it is initialized to a random value. The
   compressor should only initialize a new MSN for the initial IR or IR-
   CR packet sent for a CID that corresponds to a context that is not
   already associated with this profile. In other words, if the
   compressor reuses the same CID to compress many TCP flows one after
   the other, the MSN is not reinitialized but rather continues to
   increment monotonously.

   For context replication, the compressor does not use the MSN of the
   base context when sending the IR-CR packet, unless the replication
   process overwrites the base context (i.e. BCID == CID). Instead, the
   compressor uses the value of the MSN if it already exists in the
   context being associated with the new flow (CID); otherwise, the MSN
   is initialized to a new value.


6.3.2.  IP-ID Behavior

   The IP-ID field of the Ipv4 header can have different change
   patterns. RFC 3095 [2] describes three behaviors: sequential (NBO),
   sequential byteswapped, and random (RND). In addition, this profile
   uses a fourth behavior, the constant zero IP-ID behavior as defined
   in RFC 3843 [12] (SID).



Pelletier, et. al                                              [Page 23]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005



   The compressor monitors changes in the value of the IP-ID field for a
   number of packets, to identify which one of the above listed behavior
   is the closest match to the observed change pattern. The compressor
   can then select packet formats based the identified field behavior.

   If more than one level of IP headers is present, ROHC-TCP can assign
   a sequential behavior (NBO or byteswapped) only to the IP-ID of
   innermost IP header. This is because only this IP-ID is likely to
   have a close correlation with the MSN (see also section 6.3.1).
   Therefore, a compressor MUST assign either the constant zero IP-ID or
   the random behavior to tunneling headers.

   The IP-ID behavior control fields are transmitted in certain packet
   formats, as a two-bit field and for each IP header. When the
   compressor sends compressed packets, this control field is used to
   determine which set of packet formats will be used. Note these
   control fields are also used to determine the contents of the
   irregular chain item for each IP header.


6.3.3.  Explicit Congestion Notification (ECN) in ROHC-TCP

   When ECN is used once on a stream, it can be expected that ECN bits
   will be change quite often. ROHC-TCP maintains a control field in the
   context to indicate if ECN is used or not. This control field is
   transmitted in the dynamic chain of the TCP header, and its value can
   be updated using specific compressed headers carrying a 7-bit CRC.

   When this control field indicates that ECN is being used, items of IP
   and TCP headers in the irregular chain will include bits used for
   ECN. To preserve octet-alignment, all of the TCP reserved bits are
   transmitted and, for outer IP headers, the entire TOS/TC field is
   included in the irregular chain.

   The design rationale behind this is the possible use of the "full-
   functionality option" of section 9.1 of RFC 3168 [23].


6.4.  CRC Calculations

   The 3-bit and 7-bit CRCs both cover the entire uncompressed header
   chain. Note that there is no division between CRC-STATIC or CRC-
   DYNAMIC fields in ROHC-TCP, as opposed to profiles defined in [2].


6.5.  Initialization

   The static context of ROHC TCP streams can be initialized in either
   two ways:




Pelletier, et. al                                              [Page 24]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   1) By using an IR packet as in section 7.3, where the profile is six
   (6) and the static chain ends with the static part of a TCP header.

   2) By replicating an existing context using the mechanism defined by
   ROHC-CR. This is done with the IR-CR packet defined in section 7.4,
   where the profile number is six (6).


7. Packet Types

   ROHC-TCP defines two different packet types: the Initialization and
   Refresh (IR) packet type, and the Compressed packet type (CO). Each
   type corresponds to one of the possible states of the compressor.

   Each packet type also defines a number of packet formats: [TBD]
   packet formats are defined for compressed headers (CO), and two for
   initialization and refresh (IR).

   Finally, the profile-specific part of the IR-CR packet [3] is also
   defined in this section.


7.1. Compressed Header Chains

   Some packet types use one or more chains containing sub-header
   information. The function of a chain is to group items based on
   similar characteristics, i.e. grouping fields that either are static,
   dynamic or irregular in behavior. Chaining is done by appending each
   item to the chain in their order of appearance in the original
   header, starting from the fields in the outermost header.

   Static chain:

     The static chain is consists of one item for each header of the
     chain of headers to be compressed, starting from the outermost IP
     header and ending with a TCP header. In the formal description of
     the packet formats, this static chain item for each header type is
     named format_<protocol name>_static.

   Dynamic chain:

     The dynamic chain consists of one item for each header of the chain
     of headers to be compressed, starting from the outermost IP header
     and ending with a TCP header. It should be noted that the dynamic
     chain item for the TCP header also contains a compressed list of
     TCP options (see section 7.2). In the formal description of the
     packet formats, this dynamic chain item for each header type is
     named format_<protocol name>_dynamic.






Pelletier, et. al                                              [Page 25]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   Replicate chain:

     The replicate chain consists of one item for each header in the
     header chain to be compressed, starting from the outermost IP
     header and ending with a TCP header. It should be noted that the
     replicate chain item for the TCP header also contains a compressed
     list of TCP options (see section 7.2). In the formal description of
     the packet formats, this replicate chain item for each header type
     is named format_<protocol name>_replicate. Header fields that are
     not present in the replicate chain are replicated from the base
     context.

   Irregular chain:

     The structure of the irregular chain is analogous to the structure
     of the static chain. For each compressed packet, the irregular
     chain is appended at the specified location in the general format
     of the compressed packets as defined in section 7.5. This chain
     also includes the irregular chain items for TCP options as defined
     in section 7.2.7.

     Note that the format of the irregular chain for the innermost IP
     header differs from the format of outer IP headers, since this
     header is a part of the compressed base header. The name of the
     chain item for the innermost header is postfixed
     with_innermost_irregular, while the irregular chain item for outer
     IP headers is postfixed by_outer_irregular. The format of the
     irregular chain item for the outer IP headers also determined using
     a flag for TTL/Hoplimit; this flag can be present in some
     compressed base headers.


7.2. Compressing TCP Options with List Compression

   This section describes in details how list compression is applied to
   the TCP options.
   In the definition of the packet formats for ROHC-TCP, the most
   frequent type of TCP options are described. Each of these options has
   an uncompressed format, a format_[option_type]_list_item format and a
   format_[option_type]_irregular format, where [option_type] is the
   name of the actual field item in the option list.



7.2.1.  List Compression

   The TCP options in the uncompressed packet can be structured as an
   ordered list, whose order and presence are most of the time constant
   between packets. The generic structure of such a list is as follows:





Pelletier, et. al                                              [Page 26]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


            +--------+--------+--...--+--------+
      list: | item 1 | item 2 |       | item n |
            +--------+--------+--...--+--------+

   The basic principles of list-based compression are the following:

      1) When a context is being initialized, a complete representation
         of the compressed list of options is transmitted. All options
         that have any content are present in the compressed list of
         items sent to the decompressor.

   Then, once the context has been initialized:

      2) When the structure AND the content of the list are not
         changing, no information about the list is sent in compressed
         headers.

      3) When the structure of the list is constant, and when only the
         content of one or more options that are defined within the
         irregular format is changing, no information about the list
         needs to be sent in compressed headers; the irregular content
         is sent as part of the irregular chain (as described in section
         7.2.7) in the generalcompressed packet format (section 7.5).

      4) When the structure of the list changes, a compressed list is
         sent in the compressed header, including a representation of
         its structure and order.


7.2.2.  Table-based Item Compression

   The Table-based item compression compresses individual items sent in
   compressed lists. The compressor assigns a unique identifier,
   "Index", to each item "Item" of a list.

   Compressor Logic

      The compressor conceptually maintains an Item Table containing all
      items, indexed using "Index". The (Index, Item) pair is sent
      together in compressed lists until the compressor gains enough
      confidence that the decompressor has observed the mapping between
      items and their respective index. Confidence is obtained from the
      reception of an acknowledgment from the decompressor, or by
      sending L (Index, Item) pairs (not necessarily consecutively). The
      value for L is maintained by the compressor. Once confidence
      is obtained, the index alone is sent in compressed lists to
      indicate the presence of the item corresponding to this index.

      The compressor may reassign an existing index to a new item, by
      re-establishing the mapping using the procedure described above.




Pelletier, et. al                                              [Page 27]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   Decompressor Logic

      The decompressor conceptually maintains an Item Table that
      contains all (Index, Item) pairs received. The Item Table is
      updated whenever an (Index, Item) pair is received and
      decompression is successfully verified using the CRC. The
      decompressor retrieves the item from the table whenever an Index
      without an accompanying Item is received.


7.2.3.  Item Tables

   Compressor Logic

      The compressor uses the following structure to represent an entry
      in the Item Table:

                 +-------+------+---------+--------------------------+
         Index i | Known | Item | Counter | MSN_1, MSN_2, ..., MSN_L |
                 +-------+------+---------+--------------------------+

      The flag "Known" indicates whether the mapping between Index i and
      Item has been established, i.e., if Index i can be sent in
      compressed lists without its corresponding Item.

      The "Counter" field is useful to obtain confidence that the
      context at the decompressor contains the (Index, Item) pair.

      The list of sequence numbers, [MSN 1, ..., MSN L], is useful in
      relating an acknowledgment received from the decompressor with the
      (Index, Item) pair, meaning that it is now part of the
      decompressor context.

      The flag "Known" is initially set to a value of zero. It is also
      set to zero whenever Index i is assigned to a new Item. "Known" is
      set to a non-zero value when either of the following occur:

         a) The corresponding (Index, Item) pair is acknowledged;
         b) Counter >= L (confidence based of the optimistic approach).

      When the compressor sets the flag "Known", the list of sequence
      numbers can be discarded.

   Decompressor Logic

      The decompressor uses the following structure to represent an
      entry in the Item Table:

                 +-------+------+
         Index i | Known | item |
                 +-------+------+



Pelletier, et. al                                              [Page 28]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


      The flag "Known" is initially set to a value of zero. "Known" is
      set to a non-zero value when the decompressor receives an (Index,
      Item) pair and inserts the item "Item" into the table at position
      "Index".

      If an index without an accompanying item is received for which the
      value of the "Known" flag is zero, the header MUST be discarded
      and a NACK SHOULD be sent.


7.2.4.  Constraints to List Compression

   List compression, as defined in the ROHC-FN [4], allows 7-bit indexes
   to be used in the Item table. For ROHC-TCP, the compressor MUST use
   the low-order 4 bits of the item count (i.e. large_xi of [4], section
   5.5.5) to describe an index. In other words, the compressor MUST NOT
   map items with indexes larger than a value of 15. This is because no
   more than 16 different options are expected to be used in a TCP flow.


7.2.5.  Item Table Mappings

   The mapping between TCP option type and table indexes are listed in
   the table below:

      +-----------------+---------------+
      |   Option name   |  Table index  |
      +-----------------+---------------+
      |      NOP        |       0       |
      |      EOL        |       1       |
      |      MSS        |       2       |
      |  WINDOW SCALE   |       3       |
      |   TIMESTAMP     |       4       |
      | SACK-PERMITTED  |       5       |
      |      SACK       |       6       |
      | Generic options |      7-15     |
      +-----------------+---------------+

   Some TCP options are used more frequently than others. To simplify
   their compression, a part of the item table is reserved for these
   option types, as shown on the table above. The decompressor MUST use
   these mappings between item and indexes to decompress TCP options
   compressed using list compression.

   The compressor can thus omit from the compressed packet format an
   option type that corresponds to a reserved item in the item table.
   This is because the type of the option can be known based on the
   index number.

   It is expected that the option types for which an index is reserved
   in the item table will only appear once in a list. However, if an



Pelletier, et. al                                              [Page 29]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   option type is detected twice in the same options list and if both
   options have a different content, the compressor should compress the
   second occurrence of the option type by mapping it to a generic
   compressed option. Otherwise, if the options have the exact same
   content, the compressor can still use the same table index for both.

   The NOP option

      The NOP option can appear more than once in the list. However,
      since its value is always the same, no context information needs
      to be transmitted. Multiple NOP options can thus be mapped to the
      same index. Since the NOP option does not have any content when
      compressed as a list_item, it will never be present in the item
      list. For consistency, the compressor should still establish an
      entry in the list by setting the presence bit, as done for the
      other type of options.

   The EOL option

      The size of the compressed format for the EOL option can be larger
      than one octet, and it is defined so that it includes the option
      padding. This is because the EOL should terminate the parsing of
      the options, but it can also be followed by padding octets that
      all have the value zero.

   The Generic option

      The generic option can be used to compress any type of TCP option
      that do not have a reserved index in the item table.


7.2.6. Compressed Lists in Dynamic Chain

   When a compressed list for TCP options is part of the dynamic chain
   (i.e. IR or IR-DYN packets), the compressed list must have all its
   list items present, i.e. all x-bits in the XI list must be set.


7.2.7. Irregular Chain Items for TCP Options

   The list_item represents the option inside the compressed item list,
   and the irregular format is used for the option fields that are
   expected to change with each packet. When an item of the specified
   type is present in the current context, these irregular fields are
   present in each compressed packet, as part of the irregular chain.
   Since many of the TCP option types are expected to stay static for
   the duration of a flow, many of the irregular_formats are empty.

   The irregular chain for TCP options is structured analogously to the
   structure of the current TCP options in the uncompressed packet. If a
   compressed type 0 list is present in the compressed packet, then the



Pelletier, et. al                                              [Page 30]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   irregular chain for TCP options MUST NOT contain irregular items for
   the list items that are transmitted inside the compressed list (i.e.
   items in the list that have the x-bit set in its xi). The items that
   are not present in the compressed list, but are present in the
   current list, MUST have their respective irregular items present in
   the irregular chain.


7.2.8.  Replication of TCP Options

   The entire table of TCP options items is always replicated when using
   the IR-CR packet. In the IR-CR packet, the current list of options
   for the new flow is also transmitted as a generic compressed list in
   the IR-CR packet.


7.3.  Initialization and Refresh Packets (IR)

   ROHC-TCP uses the basic structure of the ROHC IR and IR-DYN packets
   as defined in [2] (section 5.2.3. and 5.2.4. respectively). The 8-bit
   CRC is computed according to section 5.9.1 of [2].

   o Packet type: IR

     This packet type communicates the static part and the dynamic part
     of the context.

   For the ROHC-TCP IR packet, the value of the x bit must be set to
   one. It has the following format:

     0   1   2   3   4   5   6   7
    --- --- --- --- --- --- --- ---
   :         Add-CID octet         : if for small CIDs and (CID != 0)
   +---+---+---+---+---+---+---+---+
   | 1   1   1   1   1   1   0   1 | IR type octet
   +---+---+---+---+---+---+---+---+
   :                               :
   /      0-2 octets of CID        / 1-2 octets if for large CIDs
   :                               :
   +---+---+---+---+---+---+---+---+
   |            Profile            | 1 octet
   +---+---+---+---+---+---+---+---+
   |              CRC              | 1 octet
   +---+---+---+---+---+---+---+---+
   |                               |
   /         Static chain          / variable length
   |                               |
   - - - - - - - - - - - - - - - -
   |                               |
   /        Dynamic chain          / variable length
   |                               |



Pelletier, et. al                                              [Page 31]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   - - - - - - - - - - - - - - - -
   |                               |
   /           Payload             /  variable length
   |                               |
    - - - - - - - - - - - - - - - -

      CRC: 8-bit CRC, computed according to section 5.9.1 of [2].

      Static chain: See section 7.1.
      Dynamic chain: See section 7.1.


      Payload:  The payload of the corresponding original packet, if
           any. The presence of a payload is inferred from the packet
           length.

   o Packet type: IR-DYN

     This packet type communicates the dynamic part of the context.

   The ROHC-TCP IR-DYN packet has the following format:

     0   1   2   3   4   5   6   7
    --- --- --- --- --- --- --- ---
   :         Add-CID octet         : if for small CIDs and (CID != 0)
   +---+---+---+---+---+---+---+---+
   | 1   1   1   1   1   0   0   0 | IR-DYN type octet
   +---+---+---+---+---+---+---+---+
   :                               :
   /      0-2 octets of CID        / 1-2 octets if for large CIDs
   :                               :
   +---+---+---+---+---+---+---+---+
   |            Profile            | 1 octet
   +---+---+---+---+---+---+---+---+
   |              CRC              | 1 octet
   +---+---+---+---+---+---+---+---+
   |                               |
   /     Profile_Specific_Part     / variable length
   |                               |
   - - - - - - - - - - - - - - - -
   |                               |
   /           Payload             /  variable length
   |                               |
    - - - - - - - - - - - - - - - -

      CRC: 8-bit CRC, computed according to section 5.9.1 of [2].

      Dynamic chain: See section 7.1.

      Payload:  The payload of the corresponding original packet, if
      any. The presence of a payload is inferred from the packet length.



Pelletier, et. al                                              [Page 32]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


7.4.  Context Replication Packets (IR-CR)

   Context replication requires a dedicated IR packet format that
   uniquely identifies the IR-CR packet for the ROHC-TCP profile.


   o Packet type: IR-CR

     This packet type communicates a reference to a base context along
     with the static and dynamic parts of the replicated context that
     differs from the base context.

   The ROHC-TCP IR-CR packet follows the general format of the ROHC CR
   packet, as defined in ROHC-CR [3], section 3.4.2. With consideration
   to the extensibility of the IR packet type defined in RFC 3095 [2],
   the ROHC-TCP profile supports context replication through the profile
   specific part of the IR packet. This is achieved using the bit (x)
   left in the IR packet header for "Profile specific information". For
   ROHC-TCP, this bit is defined as a flag indicating whether this
   packet is an IR packet or an IR-CR packet. For the ROHC-TCP IR-CR
   packet, the value of the x bit must be set to zero.

   The ROHC-TCP IR-CR has the following format:

     0   1   2   3   4   5   6   7
    --- --- --- --- --- --- --- ---
   :         Add-CID octet         : if for small CIDs and (CID != 0)
   +---+---+---+---+---+---+---+---+
   | 1   1   1   1   1   1   0   0 | IR-CR type octet
   +---+---+---+---+---+---+---+---+
   :                               :
   /      0-2 octets of CID        / 1-2 octets if for large CIDs
   :                               :
   +---+---+---+---+---+---+---+---+
   |            Profile            | 1 octet
   +---+---+---+---+---+---+---+---+
   |              CRC              | 1 octet
   +---+---+---+---+---+---+---+---+
   | B |          CRC7             | 1 octet
   +---+---+---+---+---+---+---+---+
   +---+---+---+---+---+---+---+---+
   :   Reserved    |   Base CID    : 1 octet, for small CID, if B=1
   +---+---+---+---+---+---+---+---+
   :                               :
   /           Base CID            / 1-2 octets, for large CIDs, if B=1
   :                               :
   +---+---+---+---+---+---+---+---+
   |                               |
   |        Replicate chain        / variable length
   |                               |
    - - - - - - - - - - - - - - - -



Pelletier, et. al                                              [Page 33]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   |                               |
   /           Payload             / variable length
   |                               |
    - - - - - - - - - - - - - - - -

      B:  B = 1 indicates that the Base CID field is present.

      CRC7: The CRC over the original, uncompressed, header. This 7-bit
          CRC is computed according to section 3.4.1.1 of [3].

      Replicate chain: See section 7.1.

      Payload:  The payload of the corresponding original packet, if
      any. The presence of a payload is inferred from the packet length.


7.5.  Compressed Packets (CO)

   The ROHC-TCP CO packets communicate irregularities in the packet
   header. All CO packets carry a CRC and can update the context.

   The general format for a compressed TCP header is as follows:

        0   1   2   3   4   5   6   7
       --- --- --- --- --- --- --- ---
      :         Add-CID octet         :  if for small CIDs and CID 1-15
      +---+---+---+---+---+---+---+---+
      |   first octet of base header  |  (with type indication)
      +---+---+---+---+---+---+---+---+
      :                               :
      /   0, 1, or 2 octets of CID    /  1-2 octets if large CIDs
      :                               :
      +---+---+---+---+---+---+---+---+
      /   remainder of base header    /  variable number of octets
      +---+---+---+---+---+---+---+---+
      :                               :
      /        Irregular Chain        /  variable
      :                               :
       --- --- --- --- --- --- --- ---
      :                               :
      /  TCP Options Irregular Part   /  variable
      :                               :
       --- --- --- --- --- --- --- ---

   The base header in the figure above is the compressed representation
   of the innermost IP header and the TCP header in the uncompressed
   packet. The full set of base headers are described in section 8.8.

   Irregular chain: See section 7.1.

   TCP options irregular part: See section 7.2.7.



Pelletier, et. al                                              [Page 34]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.  Packet Formats

   This section describes the set of compressed TCP/IP packet formats.
   The normative description of the packet formats is given using a
   formal notation, the ROHC-FN [4]. The formal description of the
   packet formats specifies all of the information needed to compress
   and decompress a header relative to the context.

   In particular, the notation provides a list of all the fields present
   in the uncompressed and compressed TCP/IP headers, and defines how to
   map from each uncompressed packet to its compressed equivalent and
   vice versa. See the ROHC-FN [4] for an explanation of the formal
   notation itself, and the encoding methods used to compress each of
   the fields in the TCP/IP header.

   Note that the formal definition of the packet formats for ROHC-TCP
   includes comments that follow a specific syntax. These comments,
   called annotations, make use of square brackets as delimiters;
   numbers in between the "[" and the "]" are used to provide additional
   information about the expected number of bits for the field(s) that
   appears as a right-hand operand. These are not normative in any way.


8.1. Design rationale for compressed base headers

   The compressed packet formats are defined as two separate sets: one
   set for the packets where the innermost IP header contains a
   sequential IP-ID (either network byte order or byte swapped), and one
   set for the packets without sequential IP-ID (either random, zero, or
   no IP-ID).

   These two sets of packet formats are referred to as the "sequential"
   and the "random" set of packet format.

   In addition, there is a common compressed packet that can be used
   regardless of the type of IP-ID behaviour. This common packet can
   transmit rarely changing fields and also send the frequently changing
   field coded in variable lengths. The common packet format can also
   change the value of control fields such as IP-ID and ECN behaviour.

   All compressed base headers contain a 3-bit CRC, unless they update
   control fields such as "ip_id_behavior" or "ecn_used" that affect the
   interpretation of subsequent packets. Packets that can modify these
   control fields will carry a 7-bit CRC instead.

   The encoding methods used in the compressed base headers are based on
   the following design criteria:

   o MSN

     Since the MSN is a number generated by the compressor, it only



Pelletier, et. al                                              [Page 35]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     needs to be large enough to ensure robust operation and to
     accommodate a small amount of reordering. Therefore, each
     compressed base header contains 4 bits of MSN. To handle
     reordering, the LSB offset value is set to p=4.

   o Sequence number

     For ROHC-TCP compression to have the capability to handle bulk data
     transfers efficiently, and for such connections, the sequence
     number is expected to increase by about 1460 bytes (which can be
     represented by 11 bits). For the compressed base headers to handle
     retransmissions (i.e. negative delta to the sequence number), the
     LSB interpretation interval must handle negative offsets about as
     large as positive offset, which means that one more bit is needed.

     Also, for ROHC-TCP to be robust to losses, two additional bits are
     added to the LSB encoding of the sequence number. This means that
     the base headers should contain at least 14 bits of LSB-encoded
     sequence number when present. According to the logic above, the LSB
     offset value p, is set to be as large as the positive offset, i.e.
     p=2^(k-1)-1.

   o Acknowledgement number

     The design criterion for the acknowledgement number is similar to
     that of the sequence number. However, often only every other data
     packet is acknowledged, which means that the expected delta value
     is twice as large as for sequence numbers. Therefore, at least 15
     bits of acknowledgement number should be used in compressed base
     headers. Since the acknowledgement number is expected to constantly
     increase, and the only exception to this is packet reordering
     (either on link or pre-link), the negative offset for LSB encoding
     is set to be 25% of the total interval, i.e. p=2^(k-2)-1. The
     offset value p has been set the same way as for the sequence number
     (p=2^(k-1)-1).

   o Window

     The TCP window field is expected to increase in increments of
     similar size as the sequence number, and therefore the design
     criterion for the TCP window has been to send at least 14 bits when
     used.

   o IP-ID

     For the "sequential" set of packet formats, all the compressed base
     headers contains LSB encoded IP-ID offset bits. The requirement is
     that at least 3 bits of IP-ID should always be present, but it is
     preferable to use 4 to 7 bits. When k=3, p=1 and if k>3, then p=3
     since the offset is expected to increase most of the time.




Pelletier, et. al                                              [Page 36]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   Each set of packet formats contains 10 different compressed base
   headers. The reason for having this large number of packets is that
   the TCP sequence number, TCP acknowledgement number, TCP window and
   MSN are frequently changing in a non-linear pattern. All of the
   compressed base headers transmit a LSB-encoded MSN, the push flag and
   a CRC, and in addition to this, all the base headers in the
   sequential packet format set contains LSB encoded IP-ID.

   The following packet formats exist in both the sequential and random
   packet format sets:

   - Format 1: This packet format transmits changes to the TCP sequence
     number and its principal use should be on the downstream of a data
     transfer.

   - Format 2: This packet format transmits the TCP sequence number in
     scaled form, and will normally be used on the downstream of a data
     transfer where the payload size is constant for multiple packets.

   - Format 3: This packet format transmits changes in the TCP
     acknowledgement number, and will be used in the acknowledgement
     direction of data transfer.

   - Format 4: This packet format is similar to format 3, but sends
     scaled Acknowledgement number.

   - Format 5: This packet format transmits both the TCP sequence number
     and the acknowledgement number, and should be particularly useful
     for streams that send data in both directions.

   - Format 6: This packet format is similar to format 5, but sends the
     sequence number in scaled form, when the payload size is static for
     certain intervals in a data stream.

   - Format 7: This packet format transmits changes to both the TCP
     sequence number and the TCP window, and is expected to be useful
     for any type of data transfer.

   - Format 8: This packet format transmits changes to both the TCP
     acknowledgement number and the TCP window, and is expected to be
     useful for the acknowledgement streams of data connections.

   - Format 9: This packet format is similar to format 7, but sends the
     sequence number in scaled form to allow higher compression rates on
     streams with a constant payload size,

   - Format 10: This packet format is used to transmit changes to some
     of the more seldom changing fields in the streams, such as ECN
     behaviour, Reset/SYN/FIN flags, the TTL/Hop Limit and the TCP
     options list. This format carries a 7-bit CRC, since it can change
     the contents of the irregular chain in later packets. Note that



Pelletier, et. al                                              [Page 37]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     this can be seen as a reduced form of the common packet format.

   - Common packet format: The common packet format can be used for all
     kinds of IP-ID behaviour, and should be used when some of the more
     rarely changing fields in the IP or TCP header changes. Since this
     packet format can be used to change what set of packet formats is
     to be used for future packets, it carries a 7-bit CRC to reduce the
     probability of context corruption. This packet can basically change
     all the dynamic fields in the IP and TCP header, and it uses a
     large set of flags to control which fields that are present in the
     packet.


8.2. Global Control Fields

   control_fields  = ecn_used,           %[  1 ]
                     msn,                %[ 16 ]
                     ip_inner_ecn,       %[  2 ]
                     seq_number_scaled,  %[ 32 ]
                     seq_number_residue, %[ 32 ]
                     ack_stride,         %[ 16 ]
                     ack_number_scaled,  %[ 16 ]
                     ack_number_residue; %[ 16 ]


8.3.  General Structures

   static_or_irreg32(flag) ===
   {
     uc_format = field; %[ 32 ]

     co_format_irreg_enc = field, %[ 32 ]
     {
       let (flag == 1);
       field ::= irregular(32);
     };

     co_format_static_enc = field, %[ 0 ]
     {
       let (flag == 0);
       field ::= static;
     };
   };

   static_or_irreg16(flag) ===
   {
     uc_format = field; %[ 16 ]

     co_format_irreg_enc = field, %[ 16 ]
     {
       let (flag == 1);



Pelletier, et. al                                              [Page 38]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       field ::= irregular(16);
     };
     co_format_static_enc = field, %[ 0 ]
     {
       let (flag == 0);
       field ::= static;
     };
   };

   static_or_irreg8(flag) ===
   {
     uc_format = field; %[ 8 ]

     co_format_irreg_enc = field, %[ 8 ]
     {
       let (flag == 1);
       field ::= irregular(8);
     };
     co_format_static_enc = field, %[ 0 ]
     {
       let (flag == 0);
       field ::= static;
     };
   };

   variable_length_32_enc(flag) ===
   {
     uc_format = field; %[ 32 ]

     co_format_not_present = field, %[ 0 ]
     {
       let(flag == 0);
       field ::= static;
     };
     co_format_8_bit = field, %[ 8 ]
     {
       let(flag == 1);
       field ::= lsb(8, 63);
     };
     co_format_16_bit = field, %[ 16 ]
     {
       let(flag == 2);
       field ::= lsb(16, 16383);
     };
     co_format_32_bit = field, %[ 32 ]
     {
       let(flag == 3);
       field ::= irregular(32);
     };
   };




Pelletier, et. al                                              [Page 39]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   variable_length_16_enc(flag) ===
   {
     uc_format = field; %[ 16 ]

     co_format_not_present = field, %[ 0 ]
     {
       let(flag == 0);
       field ::= static;
     };
     co_format_8_bit = field, %[ 8 ]
     {
       let(flag == 1);
       field ::= lsb(8, 63);
     };
     co_format_16_bit = field, %[ 16 ]
     {
       let(flag == 2);
       field ::= irregular(16);
     };
   };

   optional32 (flag) ===
   {
     uc_format = item; % 0 or 32 bits

     co_format_present = item, %[ 32 ]
     {
       let (flag == 1);
       item ::= irregular (32);
     };

     co_format_not_present = item, %[ 0 ]
     {
       let (flag == 0);
       item ::= compressed_value (0, 0);
     };
   };

   lsb_7_or_31 ===
   {
     uc_format = item; % 7 or 31 bits

     co_format_lsb_7  = discriminator, %[ 1 ]
                        item,          %[ 7 ]
     {
       discriminator ::= '0';
       item          ::= lsb (7, 8);
     };






Pelletier, et. al                                              [Page 40]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     co_format_lsb_31 = discriminator, %[ 1 ]
                        item,          %[ 31 ]
     {
       discriminator ::= '1';
       item          ::= lsb (31, 256);
     };
   };

   opt_lsb_7_or_31 (flag) ===
   {
     uc_format = item; % 32 bits

     co_format_present = item, % 8 or 32 bits
     {
       let (flag == 1);
       item ::= lsb_7_or_31;
     };

     co_format_not_present = item, %[ 0 ]
     {
       let (flag == 0);
       item ::= compressed_value (0, 0);
     };
   };

   crc3 (data_value, data_length) ===
   {
     uc_format = ;

     co_format = crc_value, %[ 3 ]
     {
       crc_value ::= crc(3, 0x06, 0x07, data_value, data_length);
     };
   };

   crc7 (data_value, data_length) ===
   {
     uc_format = ;

     co_format = crc_value, %[ 7 ]
     {
       crc_value ::= crc(7, 0x79, 0x7f, data_value, data_length);
     };
   };










Pelletier, et. al                                              [Page 41]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.4.  Extension Headers


8.4.1.  IPv6 DEST opt header

   ip_dest_opt ===
   {
     uc_format = next_header, %[ 8 ]
                 length,      %[ 8 ]
                 value;       % n bits

     default_methods =
     {
       next_header      ::= static;
       length           ::= static;
       value            ::= static;
     };

     co_format_dest_opt_static = next_header, %[ 8 ]
                                 length,      %[ 8 ]
     {
       next_header      ::= irregular(8);
       length           ::= irregular(8);
     };

     co_format_dest_opt_dynamic = value, % n bits
     {
       value ::= irregular(length:uncomp_value * 64 + 48);
     };

     co_format_dest_opt_replicate_0 = discriminator, %[ 8 ]
     {
       discriminator ::= '00000000';
     };

     co_format_dest_opt_replicate_1 = discriminator, %[ 8 ]
                                      length,        %[ 8 ]
                                      value,         % n bits
     {
       discriminator    ::= '10000000';
       length           ::= irregular(8);
       value            ::= irregular(length:uncomp_value * 64 + 48);
     };
   };










Pelletier, et. al                                              [Page 42]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.4.2.  IPv6 HOP opt header

   ip_hop_opt ===
   {
     uc_format = next_header, %[ 8 ]
                 length,      %[ 8 ]
                 value;       % n bits

     default_methods =
     {
       next_header      ::= static;
       length           ::= static;
       value            ::= static;
     };

     co_format_hop_opt_static = next_header, %[ 8 ]
                                length,      %[ 8 ]
     {
       next_header      ::= irregular(8);
       length           ::= irregular(8);
     };

     co_format_hop_opt_dynamic = value, % n bits
     {
       value ::= irregular(length:uncomp_value * 64 + 48);
     };

     co_format_hop_opt_replicate_0 = discriminator, %[ 8 ]
     {
       discriminator ::= '00000000';
     };

     co_format_hop_opt_replicate_1 = discriminator, %[ 8 ]
                                     length,        %[ 8 ]
                                     value,         % n bits
     {
       discriminator    ::= '10000000';
       length           ::= irregular(8);
       value            ::= irregular(length:uncomp_value * 64 + 48);
     };
   };


8.4.3.  IPv6 Routing Header

   ip_rout_opt ===
   {
     uc_format = next_header, %[ 8 ]
                 length,      %[ 8 ]
                 value;       % n bits




Pelletier, et. al                                              [Page 43]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     default_methods =
     {
       next_header ::= static;
       length      ::= static;
       value       ::= static;
     };

     co_format_rout_opt_static = next_header, %[ 8 ]
                                 length,      %[ 8 ]
                                 value,       % n bits
     {
       next_header ::= irregular(8);
       length      ::= irregular(8);
       value       ::= irregular(length:uncomp_value * 64 + 48);
     };

     co_format_rout_opt_dynamic =
     {
     };

     co_format_rout_opt_replicate_0 = discriminator, %[ 8 ]
     {
       discriminator  ::= '00000000';
     };

     co_format_rout_opt_replicate_1 = discriminator, %[ 8 ]
                                      length,        %[ 8 ]
                                      value,         % n bits
     {
       discriminator    ::= '10000000';
       length           ::= irregular(8);
       value            ::= irregular(length:uncomp_value * 64 + 48);
     };
   };


8.4.4.  GRE Header

   optional_checksum (flag_value) ===
   {
     uc_format = value,     % 0 or 16 bits
                 reserved1; % 0 or 16 bits

     co_format_cs_present = value,     %[ 16 ]
                            reserved1, %[ 0 ]
     {
       let (flag_value == 1);
       value     ::= irregular (16);
       reserved1 ::= uncompressed_value (16, 0);
     };




Pelletier, et. al                                              [Page 44]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     co_format_not_present = value,     %[ 0 ]
                             reserved1, %[ 0 ]
     {
       let (flag_value == 0);
       value     ::= compressed_value (0, 0);
       reserved1 ::= compressed_value (0, 0);
     };
   };

   gre_proto ===
   {
     uc_format = protocol; %[ 16 ]

     default_methods =
     {
     };

     co_format_ether_v4 = discriminator, %[ 1 ]
     {
       discriminator ::= compressed_value (1, 0);
       protocol      ::= uncompressed_value (16, 0x0800);
     };

     co_format_ether_v6 = discriminator, %[ 1 ]
     {
       discriminator ::= compressed_value (1, 1);
       protocol      ::= uncompressed_value (16, 0x86DD);
     };
   };

   gre ===
   {
     uc_format = c_flag,           %[ 1 ]
                 r_flag,           %[ 1 ]
                 k_flag,           %[ 1 ]
                 s_flag,           %[ 1 ]
                 reserved0,        %[ 9 ]
                 version,          %[ 3 ]
                 protocol,         %[ 16 ]
                 checksum_and_res, % 0 or 32 bits
                 key,              % 0 or 32 bits
                 sequence_number;  % 0 or 32 bits

     default_methods =
     {
       c_flag     ::= static;
       r_flag     ::= static;
       k_flag     ::= static;
       s_flag     ::= static;
       reserved0  ::= uncompressed_value (9, 0);
       version    ::= static;



Pelletier, et. al                                              [Page 45]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       protocol   ::= static;
       key        ::= static;
       checksum_and_res ::= optional_checksum (c_flag:uncomp_value);
     };

     co_format_gre_static = protocol, %[ 1 ]
                            c_flag,   %[ 1 ]
                            r_flag,   %[ 1 ]
                            k_flag,   %[ 1 ]
                            s_flag,   %[ 1 ]
                            version,  %[ 3 ]
                            key,      % 0 or 32 bits
     {
       protocol ::= gre_proto;
       c_flag  ::= irregular (1);
       r_flag  ::= irregular (1);
       k_flag  ::= irregular (1);
       s_flag  ::= irregular (1);
       version ::= irregular (3);
       key ::= optional32 (k_flag:uncomp_value);
       sequence_number ::= static;
     };


     co_format_gre_dynamic = checksum_and_res, % 0 or 16 bits
                             sequence_number,  % 0 or 32 bits
     {
       sequence_number ::= optional32 (s_flag:uncomp_value);
     };

     co_format_gre_replicate_0 = discriminator,    %[ 8 ]
                                 checksum_and_res, % 0 or 16 bits
                                 sequence_number,  % 0, 8 or 32 bits
     {
       discriminator ::= '00000000';
       sequence_number ::= opt_lsb_7_or_31 (s_flag:uncomp_value);
     };

     co_format_gre_replicate_1 = discriminator,    %[ 8 ]
                                 c_flag,           %[ 1 ]
                                 r_flag,           %[ 1 ]
                                 k_flag,           %[ 1 ]
                                 s_flag,           %[ 1 ]
                                 reserved,         %[ 1 ]
                                 version,          %[ 3 ]
                                 checksum_and_res, % 0 or 16 bits
                                 key,              % 0 or 32 bits
                                 sequence_number,  % 0 or 32 bits
     {
       discriminator   ::= '10000000';
       c_flag          ::= irregular (1);



Pelletier, et. al                                              [Page 46]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       r_flag          ::= irregular (1);
       k_flag          ::= irregular (1);
       s_flag          ::= irregular (1);
       reserved        ::= '0';
       version         ::= irregular (3);
       key             ::= optional32 (k_flag:uncomp_value);
       sequence_number ::= optional32 (s_flag:uncomp_value);
     };

     co_format_gre_irregular = checksum_and_res, % 0 or 16 bits
                               sequence_number,  % 0, 8 or 32 bits
     {
       sequence_number ::= opt_lsb_7_or_31 (s_flag:uncomp_value);
     };
   };


8.4.5.  MINE header

   mine ===
   {
     uc_format = next_header, %[ 8 ]
                 s_bit,       %[ 1 ]
                 res_bits,    %[ 7 ]
                 checksum,    %[ 16 ]
                 orig_dest,   %[ 32 ]
                 orig_src;    %  0 or 32 bits

     default_methods =
     {
       next_header ::= static;
       s_bit       ::= static;
       res_bits    ::= static;
       checksum    ::= inferred_mine_header_checksum;
       orig_dest   ::= static;
       orig_src    ::= static;
     };

     co_format_mine_static = next_header, %[ 8 ]
                             s_bit,       %[ 1 ]
                             res_bits,    %[ 7 ]
                             orig_dest,   %[ 32 ]
                             orig_src,    %  0 or 32 bits
     {
       next_header ::= irregular (8);
       s_bit       ::= irregular (1);
       res_bits    ::= irregular (7);
                        % include reserved - no benefit in removing them
       orig_dest   ::= irregular (32);
       orig_src    ::= optional32 (s_bit:uncomp_value);
     };



Pelletier, et. al                                              [Page 47]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     co_format_mine_dynamic =
     {
     };

     co_format_mine_replicate_0 = discriminator, %[ 8 ]
                                  checksum,      %[ 0 ]
     {
       discriminator ::= '00000000';
     };

     co_format_mine_replicate_1 = discriminator, %[ 8 ]
                                  s_bit,         %[ 1 ]
                                  res_bits,      %[ 7 ]
                                  orig_dest,     %[ 32 ]
                                  orig_src,      % 0 or 32 bits
     {
       discriminator ::= '10000000';
       s_bit         ::= irregular (1);
       res_bits      ::= irregular (7);
       orig_dest     ::= irregular (32);
       orig_src      ::= optional32 (s_bit:uncomp_value);
     };
   };


8.4.6.  Authentication Header (AH) header

   ah ===
   {
     uc_format = next_header,     %[ 8 ]
                 length,          %[ 8 ]
                 res_bits,        %[ 16 ]
                 spi,             %[ 32 ]
                 sequence_number, %[ 32 ]
                 auth_data;       % n bits

     default_methods =
     {
       next_header     ::= static;
       length          ::= static;
       res_bits        ::= static;
       spi             ::= static;
       sequence_number ::= static;
       auth_data       ::= irregular (length:uncomp_value * 32 - 32);
     };

     co_format_ah_static = next_header, %[  8 ]
                           length,      %[  8 ]
                           spi,         %[ 32 ]
     {
       next_header ::= irregular(8);



Pelletier, et. al                                              [Page 48]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       length      ::= irregular (8);
       spi         ::= irregular (32);
     };

     co_format_ah_dynamic = res_bits,        %[ 16 ]
                            sequence_number, %[ 32 ]
                            auth_data,       %  n bits
     {
       res_bits        ::= irregular (16);
       sequence_number ::= irregular (32);
     };

     co_format_ah_replicate_0 = discriminator,   %[ 8 ]
                                sequence_number, % 8 or 32 bits
                                auth_data,       % n bits
     {
       discriminator   ::= '00000000';
       sequence_number ::= lsb_7_or_31;
     };

     co_format_ah_replicate_1 = discriminator,   %[ 8 ]
                                length,          %[ 8 ]
                                res_bits,        %[ 16 ]
                                spi,             %[ 32 ]
                                sequence_number, %[ 32 ]
                                auth_data,       %  n bits
     {
       discriminator   ::= '10000000';
       length          ::= irregular (8);
       res_bits        ::= irregular (16);
       spi             ::= irregular (32);
       sequence_number ::= irregular (32);
     };

     co_format_ah_irregular = sequence_number, % 8 or 32 bits
                              auth_data,       % n bits
     {
       sequence_number ::= lsb_7_or_31;
     };
   };


8.4.7.  Encapsulation Security Payload (ESP) header

   esp_null ===
   {
     uc_format = spi,             %[ 32 ]
                 sequence_number, %[ 32 ]
                 next_header;     %[ 8 ]

     default_methods =



Pelletier, et. al                                              [Page 49]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     {
       spi         ::= static;
               % Next header will always be present in the trailer part,
               % but sometimes it will ALSO be present in the header
               % (static chain only).
       nh_field ::= static; % Control field
       next_header ::= static;
       sequence_number ::= static;
     };

     co_format_esp_static = nh_field, %[ 8 ]
                            spi,      %[ 32 ]
     {
                      % identify next header assume next 96 bits skipped
                      % to get to end of packet (i.e. this is anchored
                      %from the end of the packet, not the start)
       nh_field ::= compressed_value(8, next_header:uncomp_value);
       next_header ::= irregular (8); % At packet end!
       spi ::= irregular (32);
     };

     co_format_esp_dynamic = sequence_number, %[ 32 ]
     {
       sequence_number  ::= irregular (32);
     };

     co_format_esp_replicate_0 = discriminator,   %[ 8 ]
                                 sequence_number, % 8 or 32 bits
     {
       discriminator   ::= '00000000';
       sequence_number ::= lsb_7_or_31;
     };

     co_format_esp_replicate_1 = discriminator,   %[ 8 ]
                                 spi,             %[ 32 ]
                                 sequence_number, %[ 32 ]
     {
       discriminator   ::= '10000000';
       spi             ::= irregular (32);
       sequence_number ::= irregular (32);
     };

     co_format_esp_irregular = sequence_number, % 8 or 32 bits
     {
       sequence_number ::= lsb_7_or_31;
     };
   };







Pelletier, et. al                                              [Page 50]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.5.  IP Header

8.5.1. Structures Common for IPv4 and IPv6

   irreg_tos_tc ===
   {
     uc_format = tos_tc; %[ 6 ]

     co_format_tos_tc_present = tos_tc, %[ 6 ]
     {
       let(ecn_used:uncomp_value == 1);
       tos_tc  ::= irregular (6);
     };

     co_format_tos_tc_not_present = tos_tc, %[ 0 ]
     {
       let(ecn_used:uncomp_value == 0);
       tos_tc  ::= static;
     };
   };

   ip_irreg_ecn ===
   {
     uc_format = ip_ecn_flags; %[ 2 ]

     co_format_tc_present = ip_ecn_flags, %[ 2 ]
     {
       let(ecn_used:uncomp_value == 1);
       ip_ecn_flags ::= irregular (2);
     };

     co_format_tc_not_present = ip_ecn_flags, %[ 0 ]
     {
       let(ecn_used:uncomp_value == 0);
       ip_ecn_flags ::= static;
     };
   };


8.5.2.  IPv6 Header

   fl_enc ===
   {
     uc_format = flow_label;

     co_format_fl_zero = discriminator, %[ 1 ]
                         flow_label,    %[ 0 ]
                         reserved,      %[ 4 ]
     {
       discriminator ::= '0';
       flow_label    ::= uncompressed_value (20, 0);



Pelletier, et. al                                              [Page 51]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       reserved      ::= '0000';
     };

     co_format_fl_non_zero = discriminator, %[ 1 ]
                             flow_label,    %[ 20 ]
     {
       discriminator ::= '1';
       flow_label    ::= irregular (20);
     };
   };

   % The argument flag should only be used if this
   % flag was set when processing a compressed base
   % header, if not, the flag should be zero.
   ipv6 (ttl_irregular_chain_flag) ===
   {
     uc_format = version,        %[   4 ]
                 tos_tc,         %[   6 ]
                 ip_ecn_flags,   %[   2 ]
                 flow_label,     %[  20 ]
                 payload_length, %[  16 ]
                 next_header,    %[   8 ]
                 ttl_hopl,       %[   8 ]
                 src_addr,       %[ 128 ]
                 dst_addr;       %[ 128 ]

     default_methods =
     {
       version        ::= uncompressed_value (4, 6);
       tos_tc         ::= static;
       ip_ecn_flags   ::= static;
       flow_label     ::= static;
       payload_length ::= inferred_ip_v6_length;
       next_header    ::= static;
       ttl_hopl       ::= static;
       src_addr       ::= static;
       dst_addr       ::= static;
     };

     co_format_ipv6_static = version_flag, %[ 1 ]
                             reserved,     %[ 2 ]
                             flow_label,   % 5 or 21 bits
                             next_header,  %[ 8 ]
                             src_addr,     %[ 128 ]
                             dst_addr,     %[ 128 ]
     {
       version_flag        ::=   '1';
       reserved            ::=   '00';
       flow_label          ::=   fl_enc;
       next_header         ::=   irregular (8);
       src_addr            ::=   irregular(128);



Pelletier, et. al                                              [Page 52]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       dst_addr            ::=   irregular(128);
     };

     co_format_ipv6_dynamic = tos_tc,       %[ 6 ]
                              ip_ecn_flags, %[ 2 ]
                              ttl_hopl,     %[ 8 ]
     {
       tos_tc       ::= irregular (6);
       ip_ecn_flags ::= irregular (2);
       ttl_hopl     ::= irregular (8);
     };

     co_format_ipv6_replicate = tos_tc,       %[ 6 ]
                                ip_ecn_flags, %[ 2 ]
     {
       tos_tc       ::= irregular (6);
       ip_ecn_flags ::= irregular (2);
     };

     co_format_ipv6_outer_irregular_without_ttl
                                       = tos_tc,       % 0 or 6 bits
                                         ip_ecn_flags, % 0 or 2 bits
     {
                 % for 'outer' headers only, irregular chain is required
       tos_tc        ::= irreg_tos_tc;
       ip_ecn_flags  ::= ip_irreg_ecn;
       let(ttl_irregular_chain_flag == 0);
     };

     co_format_ipv6_outer_irregular_with_ttl
                                       = tos_tc,       % 0 or 6 bits
                                         ip_ecn_flags, % 0 or 2 bits
                                         ttl_hopl,     %[ 8 ]
     {
                 % for 'outer' headers only, irregular chain is required
       tos_tc        ::= irreg_tos_tc;
       ip_ecn_flags  ::= ip_irreg_ecn;
       let(ttl_irregular_chain_flag == 1);
       ttl_hopl       ::= irregular(8);
     };

         % Note that the ECN bits are stored in the global control field
         % so that they can be output in TCP irregular chain.
     co_format_ipv6_innermost_irregular =
     {
       let(ip_inner_ecn:uncomp_value ==
       ip_ecn_flags:uncomp_value);
     };
   };





Pelletier, et. al                                              [Page 53]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.5.3.  IPv4 Header

   ip_id_enc_dyn (behavior) ===
   {
     uc_format = ip_id; %[ 16 ]

     co_format_ip_id_seq = ip_id, %[ 16 ]
     {
       let ((behavior == 0) || (behavior == 1) || (behavior == 2));
       % In dynamic chain, but random, seq, and seq-swapped are 16 bits
       ip_id ::= irregular(16);
     };

     co_format_ip_id_zero = ip_id, %[ 0 ]
     {
       let (behavior == 3);
       % Zero IPID
       ip_id ::= uncompressed_value (16, 0);
     };
   };

   ip_id_enc_irreg (behavior) ===
   {
     uc_format = ip_id; %[ 16 ]

     co_format_ip_id_seq = ip_id, %[ 0 ]
     {
       let (behavior == 0); % sequential
       ip_id ::= static;    % Nothing to send in irregular chain
     };

     co_format_ip_id_seq_swapped = ip_id, %[ 0 ]
     {
       let (behavior == 1); % sequential-swapped
       ip_id ::= static;    % Nothing to send in irregular chain
     };

     co_format_ip_id_rand = ip_id, %[ 16 ]
     {
       let (behavior == 2); % random
       ip_id ::= irregular (16);
     };

     co_format_ip_id_zero = ip_id, %[ 0 ]
     {
       let (behavior == 3); % zero
       ip_id ::= uncompressed_value (16, 0);
     };
   };





Pelletier, et. al                                              [Page 54]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   ip_id_behavior_enc ===
   {
     uc_format = ip_id_behavior; %[ 2 ]

     default_methods =
     {
       ip_id_behavior ::= irregular(2);
     }

     co_format_sequential = ip_id_behavior, %[ 2 ]
     {
       let (ip_id_behavior:uncomp_value = 0b00);
     };

     co_format_sequential_swapped = ip_id_behavior, %[ 2 ]
     {
       let (ip_id_behavior:uncomp_value = 0b01);
     };

     co_format_random = ip_id_behavior, %[ 2 ]
     {
       let (ip_id_behavior:uncomp_value = 0b10);
     };

     co_format_zero = ip_id_behavior, %[ 2 ]
       {
       let (ip_id_behavior:uncomp_value = 0b11);
     };
   };

   % The argument flag should only be used if this flag was
   % set when processing a compressed base header, if not,
   % the flag should be zero.

   ipv4 (ttl_irregular_chain_flag) ===
   {
     uc_format = version,      %[ 4 ]
                 hdr_length,   %[ 4 ]
                 tos_tc,       %[ 6 ]
                 ip_ecn_flags, %[ 2 ]
                 length,       %[ 16 ]
                 ip_id,        %[ 16 ]
                 rf,           %[ 1 ]
                 df,           %[ 1 ]
                 mf,           %[ 1 ]
                 frag_offset,  %[ 13 ]
                 ttl_hopl,     %[ 8 ]
                 protocol,     %[ 8 ]
                 checksum,     %[ 16 ]
                 src_addr,     %[ 32 ]
                 dst_addr;     %[ 32 ]



Pelletier, et. al                                              [Page 55]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     control_fields  = ip_id_behavior; %[ 2 ]

     default_methods =
     {
       version          ::= static;
       hdr_length       ::= uncompressed_value (4, 5);
       protocol         ::= static;
       tos_tc           ::= static;
       ip_ecn_flags     ::= static;
       ttl_hopl         ::= static;
       df               ::= static;
       mf               ::= uncompressed_value (1, 0);
       rf               ::= static;
       frag_offset      ::= uncompressed_value (13, 0);
       ip_id            ::= uncompressed_value (16, 0);
       ip_id_behavior   ::= static;
       src_addr         ::= static;
       dst_addr         ::= static;
       checksum         ::= inferred_ip_v4_header_checksum;
       length           ::= inferred_ip_v4_length;
     };

     co_format_ipv4_static = version_flag, %[ 1 ]
                             reserved,     %[ 7 ]
                             protocol,     %[ 8 ]
                             src_addr,     %[ 32 ]
                             dst_addr,     %[ 32 ]
     {
       version_flag     ::= '0';
       reserved         ::= '0000000';
       protocol         ::=  irregular (8);
       src_addr         ::=  irregular(32);
       dst_addr         ::=  irregular(32);
     };

     co_format_ipv4_dynamic = reserved,       %[ 5 ]
                              df,             %[ 1 ]
                              ip_id_behavior, %[ 2 ]
                              tos_tc,         %[ 6 ]
                              ip_ecn_flags,   %[ 2 ]
                              ttl_hopl,       %[ 8 ]
                              ip_id,          % 0/16 bits
     {
       reserved       ::= '00000';
                                         % The compressor chooses
                                         % behavior of IP-ID
                                         %   00 = sequential
                                         %   01 = sequential byteswapped
                                         %   10 = random
                                         %   11 = zero
       ip_id_behavior ::= ip_id_behavior_enc;



Pelletier, et. al                                              [Page 56]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       df             ::= irregular (1);
       tos_tc         ::= irregular (6);
       ip_ecn_flags   ::= irregular (2);
       ttl_hopl       ::= irregular (8);
       ip_id          ::= ip_id_enc_dyn (ip_id_behavior:uncomp_value);
     };

     co_format_ipv4_replicate_0 = discriminator, %[ 8 ]
                                  ip_id,         % 0 or 16 bits
                                  tos_tc,        %[ 6 ]
                                  ip_ecn_flags,  %[ 2 ]
     {
       discriminator  ::= '00000000';
       ip_id_behavior ::= static;
       ip_id          ::= ip_id_enc_irreg (ip_id_behavior:uncomp_value);
       tos_tc         ::= irregular (6);
       ip_ecn_flags   ::= irregular (2);
     };

     co_format_ipv4_replicate_1 = discriminator,  %[ 5 ]
                                  df,             %[ 1 ]
                                  ip_id_behavior, %[ 2 ]
                                  tos_tc,         %[ 6 ]
                                  ip_ecn_flags,   %[ 2 ]
                                  ttl_hopl,       %[ 8 ]
                                  ip_id,          % 0/16 bits
     {
       discriminator  ::= '10000';
       df             ::= irregular (1);
       tos_tc         ::= irregular (6);
       ip_ecn_flags   ::= irregular (2);
       ttl_hopl       ::= irregular (8);
                                         % The compressor chooses
                                         % behavior of IP-ID
                                         %   00 = sequential
                                         %   01 = sequential byteswapped
                                         %   10 = random
                                         %   11 = zero
       ip_id_behavior ::= ip_id_behavior_enc;
       ip_id ::= ip_id_enc_dyn (ip_id_behavior:uncomp_value);
     };

     co_format_ipv4_outer_irregular_without_ttl =
                                       ip_id,        % 0 or 16 bits
                                       tos_tc,       % 0 or 6 bits
                                       ip_ecn_flags, % 0 or 2 bits
     {
       ip_id_behavior ::= static;
       ip_id          ::= ip_id_enc_irreg (ip_id_behavior:uncomp_value);
       tos_tc         ::= irreg_tos_tc;
       ip_ecn_flags   ::= ip_irreg_ecn;



Pelletier, et. al                                              [Page 57]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       let(ttl_irregular_chain_flag == 0);
     };

     co_format_ipv4_outer_irregular_with_ttl =
                                       ip_id,        % 0 or 16 bits
                                       tos_tc,       % 0 or 6 bits
                                       ip_ecn_flags, % 0 or 2 bits
                                       ttl_hopl,     %[ 8 ]
     {
       ip_id_behavior ::= static;
       ip_id          ::= ip_id_enc_irreg (ip_id_behavior:uncomp_value);
       tos_tc         ::= irreg_tos_tc;
       ip_ecn_flags   ::= ip_irreg_ecn;
       let(ttl_irregular_chain_flag == 1);
       ttl_hopl       ::= irregular(8);
     };

   % Note that the ECN bits are stored in the global control field
   % so that they can be output in TCP irregular chain.
     co_format_ipv4_innermost_irregular = ip_id, % 0 or 16 bits
     {
       ip_id_behavior ::= static;
       ip_id          ::= ip_id_enc_irreg (ip_id_behavior:uncomp_value);
       let(ip_inner_ecn:uncomp_value ==
       ip_ecn_flags:uncomp_value);
     };
   };


8.6. TCP Header

   port_replicate(flags) ===
   {
     uc_format  =   port;        %[ 16 ]

     co_format_port_static_enc   = port,      %[ 0 ]
     {
       let(flags == 0b00);
       port          ::= static;
     };

     co_format_port_lsb8         = port,      %[ 8 ]
     {
       let(flags == 0b01);
       port          ::= lsb (8, 64);
     };

     co_format_port_irr_enc      = port,      %[ 16 ]
     {
       let(flags == 0b10);
       port          ::= irregular (16);



Pelletier, et. al                                              [Page 58]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     };
   };

   zero_or_irr16_enc(flag) ===
   {
     uc_format = field; %[ 16 ]

     co_format_non_zero = field, %[ 16 ]
     {
       let(flag == 0);
       field ::= irregular (16);
     };

     co_format_zero = field, %[ 0 ]
     {
       let(flag == 1);
       field ::= uncompressed_value (16, 0);
     };
   };

   ack_enc_dyn(flag) ===
   {
     uc_format = ack_number; %[ 32 ]

     co_format_ack_non_zero = ack_number, %[ 32 ]
     {
       let(flag == 0);
       ack_number ::= irregular (32);
     };

     co_format_ack_zero = ack_number, %[ 0 ]
     {
       let(flag == 1);
       ack_number ::= uncompressed_value (32, 0);
     };
   };

   tcp_ecn_flags_enc ===
   {
     uc_format = tcp_ecn_flags; %[ 2 ]

     co_format_irreg = tcp_ecn_flags, %[ 2 ]
     {
       let(ecn_used:uncomp_value == 1);
       tcp_ecn_flags ::= irregular(2);
     };

     co_format_unused =
       {
       let(ecn_used:uncomp_value == 0);
       tcp_ecn_flags ::= static;



Pelletier, et. al                                              [Page 59]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     };
   };

   tcp_res_flags_enc ===
   {
     uc_format = tcp_res_flags; %[ 4 ]

     co_format_irreg = tcp_res_flags, %[ 4 ]
     {
       let(ecn_used:uncomp_value == 1);
       tcp_res_flags     ::= irregular(4);
     };

     co_format_unused =
     {
       let(ecn_used:uncomp_value == 0);
       tcp_res_flags     ::= uncompressed_value(4, 0);
     };
   };

   tcp_irreg_ip_ecn ===
   {
     uc_format = ip_ecn_flags;     %[ 2 ]

     co_format_tc_present = ip_ecn_flags,       %[ 2 ]
     {
       let(ecn_used:uncomp_value == 1);
       ip_ecn_flags ::= compressed_value(2, ip_inner_ecn:uncomp_value);
     };

     co_format_tc_not_present = ip_ecn_flags, %[ 0 ]
     {
       let(ecn_used:uncomp_value == 0);
       ip_inner_ecn ::= static; % Global control field
       ip_ecn_flags ::= compressed_value(0,0); % Nothing transmit
     };
   };

   rsf_index_enc ===
   {
     uc_format = rsf_flag; %[ 3 ]

     co_format_none     = rsf_idx, %[ 2 ]
     {
       rsf_idx  ::= '00';
       rsf_flag ::= uncompressed_value (3, 0x00);
     };

     co_format_rst_only = rsf_idx, %[ 2 ]
     {
       rsf_idx  ::= '01';



Pelletier, et. al                                              [Page 60]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       rsf_flag ::= uncompressed_value (3, 0x04);
     };

     co_format_syn_only = rsf_idx, %[ 2 ]
     {
       rsf_idx  ::= '10';
       rsf_flag ::= uncompressed_value (3, 0x02);
     };

     co_format_fin_only = rsf_idx, %[ 2 ]
     {
       rsf_idx  ::= '11';
       rsf_flag ::= uncompressed_value (3, 0x01);
     };
   };

   optional_2bit_padding(used_flag) ===
   {
     uc_format = ;

     co_format_used = padding, %[ 2 ]
     {
       let(used_flag == 1);
       padding ::= compressed_value (2, 0x0);
     };

     co_format_unused = padding,
     {
       let(used_flag == 0);
       padding ::= compressed_value (0, 0x0);
     };
   };

   tcp ===
   {
     uc_format = src_port,      %[ 16 ]
                 dst_port,      %[ 16 ]
                 seq_number,    %[ 32 ]
                 ack_number,    %[ 32 ]
                 data_offset,   %[ 4 ]
                 tcp_res_flags, %[ 4 ]
                 tcp_ecn_flags, %[ 2 ]
                 urg_flag,      %[ 1 ]
                 ack_flag,      %[ 1 ]
                 psh_flag,      %[ 1 ]
                 rsf_flags,     %[ 3 ]
                 window,        %[ 16 ]
                 checksum,      %[ 16 ]
                 urg_ptr,       %[ 16 ]
                 options;       %  n bits




Pelletier, et. al                                              [Page 61]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     default_methods =
     {
       src_port      ::= static;
       dst_port      ::= static;
       seq_number    ::= static;
       ack_number    ::= static;
       rsf_flags     ::= static;
       psh_flag      ::= irregular (1);
       urg_flag      ::= static;
       ack_flag      ::= uncompressed_value (1, 1);
       urg_ptr       ::= static;
       window        ::= static;
       checksum      ::= irregular (16);
       tcp_ecn_flags ::= static;
       tcp_res_flags ::= static;
     };

     co_format_tcp_static = src_port, %[ 16 ]
                            dst_port, %[ 16 ]
     {
       src_port      ::=   irregular(16);
       dst_port      ::=   irregular(16);
     };

     co_format_tcp_dynamic = ecn_used,        %[ 1 ]
                             ack_stride_zero, %[ 1 ]
                             ack_zero,        %[ 1 ]
                             urp_zero,        %[ 1 ]
                             tcp_res_flags,   %[ 4 ]
                             tcp_ecn_flags,   %[ 2 ]
                             urg_flag,        %[ 1 ]
                             ack_flag,        %[ 1 ]
                             psh_flag,        %[ 1 ]
                             rsf_flags,       %[ 3 ]
                             msn,             %[ 16 ]
                             seq_number,      %[ 32 ]
                             ack_number,      %  0 or 32 bits
                             window,          %[ 16 ]
                             checksum,        %[ 16 ]
                             urg_ptr,         %  0 or 16 bits
                             ack_stride,      %  0 or 16 bits
                             options,         %  n bits
     {
       ecn_used          ::= irregular (1);
       ack_stride_zero   ::= irregular (1);
       ack_zero          ::= irregular (1);
       urp_zero          ::= irregular (1);
       ack_flag          ::= irregular (1);
       urg_flag          ::= irregular (1);
       psh_flag          ::= irregular (1);
       tcp_ecn_flags     ::= irregular (2);



Pelletier, et. al                                              [Page 62]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       rsf_flags         ::= irregular (3);
       tcp_res_flags     ::= irregular (4);
       msn               ::= irregular (16);
       seq_number        ::= irregular (32);
       window            ::= irregular (16);
       checksum          ::= irregular (16);
       urg_ptr           ::= zero_or_irr16_enc(urp_zero:comp_value);
       ack_number        ::= ack_enc_dyn(ack_zero:comp_value);
       ack_stride    ::= zero_or_irr16_enc(ack_stride_zero:comp_value);
       data_offset   ::= uncompressed_value(4, data_offset_value);
       options       ::= list_tcp_options((data_offset_value - 5) * 32);
     };

     co_format_tcp_replicate = reserved,          %[ 2 ]
                               window_presence,   %[ 1 ]
                               list_present,      %[ 1 ]
                               src_port_presence, %[ 2 ]
                               dst_port_presence, %[ 2 ]
                               ack_presence,      %[ 1 ]
                               urp_presence,      %[ 1 ]
                               urg_flag,          %[ 1 ]
                               ack_flag,          %[ 1 ]
                               psh_flag,          %[ 1 ]
                               rsf_flags,         %[ 2 ]
                               ecn_used,          %[ 1 ]
                               msn,               %[ 16 ]
                               seq_number,        %[ 32 ]
                               src_port,          %  0, 8 or 16 bits
                               dst_port,          %  0, 8 or 16 bits
                               window,            %  0 or 16 bits
                               urg_point,         %  0 or 16 bits
                               ack_number,        %  0 or 32 bits
                               ecn_padding,       %  0 or 2 bits
                               tcp_res_flags,     %  0 or 4 bits
                               tcp_ecn_flags,     %  0 or 2 bits
                               options,           %  n bits
     {
       reserved            ::=   '000';
       list_present        ::=   irregular (1);
       msn                 ::=   irregular (16);
       urg_flag            ::=   irregular (1);
       ack_flag            ::=   irregular (1);
       psh_flag            ::=   irregular (1);
       rsf_flags           ::=   rsf_index_enc;
       ecn_used            ::=   irregular (1);

       src_port_presence ::= compressed_value(2,
                                              src_port_presence_value);
       dst_port_presence ::= compressed_value(2,
                                              dst_port_presence_value);
       src_port         ::=  port_replicate(src_port_presence_value);



Pelletier, et. al                                              [Page 63]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       dst_port         ::=  port_replicate( dst_port_presence_value);
       seq_number       ::=  irregular(32);
       ack_presence     ::=  compressed_value(1, ack_presence_value);
       window_presence  ::=  compressed_value(1, window_presence_value);
       urp_presence     ::=  compressed_value(1, urg_presence_value);
       ack_number       ::=  static_or_irreg32(ack_presence_value);
       window           ::=  static_or_irreg16(window_presence_value);
       urg_point        ::=  static_or_irreg16(urp_presence_value);
       ecn_padding      ::=  optional_2bit_padding(ecn_used:comp_value);
       tcp_res_flags    ::=  tcp_res_flags_enc;
       tcp_ecn_flags    ::=  tcp_ecn_flags_enc;
       data_offset      ::=  uncompressed_value(4, data_offset_value);
       options          ::=  tcp_list_presence_enc
                             ((data_offset_value - 5) * 32,
                               list_present:comp_value,
                               ack_number:uncomp_value);
     };

   % ECN from innermost IP header is taken from global control field.
     co_format_tcp_irregular = ip_ecn_flags,  % 0 or 2 bits
                               tcp_res_flags, % 0 or 4 bits
                               tcp_ecn_flags, % 0 or 2 bits
                               checksum,      %[ 16 ]
     {
       ip_ecn_flags   ::=  tcp_irreg_ip_ecn;
       tcp_ecn_flags  ::=  tcp_ecn_flags_enc;
       tcp_res_flags  ::=  tcp_res_flags_enc;
       checksum       ::=  irregular (16);
     };
   };


8.7. TCP Options

   tcp_opt_eol(nbits) ===   {

     uc_format = type,    %[ 8 ]
                 padding; % (nbits - 8) bits

     default_methods =
     {
       type    ::= uncompressed_value (8, 0);
       pad_len ::= static;
       padding ::= uncompressed_value (nbits - 8, 0);
     };

     co_format_eol_list_item = pad_len, %  8 bits
                               padding, %[ 0 ]
     {
       pad_len ::= compressed_value(8, nbits - 8);
     };



Pelletier, et. al                                              [Page 64]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     co_format_eol_irregular =
     {
       let(nbits - 8 == pad_len:uncomp_value);
     };
   };

   tcp_opt_nop ===
   {
     uc_format = type; %[ 8 ]

     default_methods =
     {
       type ::= uncompressed_value (8, 1);
     };

     co_format_nop_list_item =
     {
     };

     co_format_nop_irregular =
     {
     };
   };

   tcp_opt_mss ===
   {
     uc_format = type,   %[ 8 ]
                 length, %[ 8 ]
                 mss;    %[ 16 ]

     default_methods =
     {
       type   ::= uncompressed_value (8, 2);
       length ::= uncompressed_value (8, 4);
       mss    ::= static;
     };

     co_format_mss_list_item = mss, %[ 16 ]
     {
       mss ::= irregular (16);
     };

     co_format_mss_irregular =
     {
     };
   };


   tcp_opt_wscale ===
   {
     uc_format = type,   %[ 8 ]



Pelletier, et. al                                              [Page 65]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


                 length, %[ 8 ]
                 wscale; %[ 8 ]

     default_methods =
     {
       type    ::= uncompressed_value (8, 3);
       length  ::= uncompressed_value (8, 3);
       wscale  ::= static;
     };

     co_format_wscale_list_item = wscale, %[ 8 ]
     {
       wscale ::= irregular (8);
     };

     co_format_wscale_irregular =
     {
     };
   };


   ts_lsb ===
   {
     uc_format = tsval;

                % Few bits (7 and 14) bits
                % can only increase, while
                % the larger formats allow
                % decreasing timestamp to
                % allow prelink reordering.
     co_format_tsval_7 = discriminator, %[ 1 ]
                         tsval,         %[ 7 ]
     {
       discriminator ::= '0';
       tsval         ::= lsb (7, -1);
     };

     co_format_tsval_14 = discriminator, %[ 2 ]
                          tsval,         %[ 14 ]
     {
       discriminator ::= '10';
       tsval         ::= lsb (14, -1);
     };

     co_format_tsval_21 = discriminator, %[ 3 ]
                          tsval,         %[ 21 ]
     {
       discriminator ::= '110';
       tsval         ::= lsb (21, 0x00040000);
     };




Pelletier, et. al                                              [Page 66]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     co_format_tsval_29 = discriminator, %[ 3 ]
                          tsval,         %[ 29 ]
     {
       discriminator ::= '111';
       tsval         ::= lsb (29, 0x04000000);
     };
   };

   tcp_opt_tsopt ===
   {
     uc_format = type,   %[ 8 ]
                 length, %[ 8 ]
                 tsval,  %[ 32 ]
                 tsecho; %[ 32 ]

     default_methods =
     {
       type   ::= uncompressed_value (8, 8);
       length ::= uncompressed_value (8, 10);
     };

     co_format_tsopt_list_item = tsval,  %[ 32 ]
                                 tsecho, %[ 32 ]
     {
       tsval  ::= irregular (32);
       tsecho ::= irregular (32);
     };

     co_format_tsopt_irregular = tsval,  % 16, 24 or 32 bits
                                 tsecho, % 16, 24 or 32 bits
     {
       tsval  ::= ts_lsb;
       tsecho ::= ts_lsb;
     };
   };

   sack_var_length_enc (base) ===
   {
     uc_format = sack_field; %[ 32 ]

     default_methods =
     {
       let (sack_offset:uncomp_value == sack_field:uncomp_value - base);
       let (sack_offset:uncomp_length == 32);
       let (sack_field:uncomp_length == 32);
     };

     co_format_lsb_15 = discriminator, %[ 1 ]
                        sack_offset,   %[ 15 ]
     {
       discriminator    ::= '0';



Pelletier, et. al                                              [Page 67]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       sack_offset      ::= lsb (15, -1);
     };

     co_format_lsb_22 = discriminator, %[ 2 ]
                        sack_offset,   %[ 22 ]
     {
       discriminator    ::= '10';
       sack_offset      ::= lsb (22, -1);
     };

     co_format_lsb_30 = discriminator, %[ 2 ]
                        sack_offset,   %[ 30 ]
     {
       discriminator    ::= '11';
       sack_offset      ::= lsb (30, -1);
     };
   };

   tcp_opt_sack_block (prev_block_end) ===
   {
     uc_format = block_start, %[ 32 ]
                 block_end;   %[ 32 ]

     co_format_0 = block_start, % 16, 24 or 32 bits
                   block_end,   % 16, 24 or 32 bits
     {
       block_start ::= sack_var_length_enc (prev_block_end);
       block_end   ::= sack_var_length_enc (block_start);
     };
   };

   tcp_opt_sack(ack_value) ===
   {
   % The ACK value from the TCP header is needed as input parameter.
     uc_format = type,    %[ 8 ]
                 length,  %[ 8 ]
                 block_1, %[ 64 ]
                 block_2, % 0 or 64 bits
                 block_3, % 0 or 64 bits
                 block_4; % 0 or 64 bits

     default_methods =
     {
       length  ::= static;
       type    ::= uncompressed_value (8, 5);
       block_2 ::= uncompressed_value (0, 0);
       block_3 ::= uncompressed_value (0, 0);
       block_4 ::= uncompressed_value (0, 0);
     };





Pelletier, et. al                                              [Page 68]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   co_format_sack1_list_item = discriminator,
                                 block_1,
     {
       let(length:uncomp_value == 10);
       discriminator ::= '00000001';
       block_1 ::= tcp_opt_sack_block (ack_value);
     };

     co_format_sack2_list_item = discriminator,
                                 block_1,
                                 block_2,
     {
       let(length:uncomp_value == 18);
       discriminator ::= '00000010';
       block_1 ::= tcp_opt_sack_block (ack_value);
       block_2 ::= tcp_opt_sack_block (block_1_end:uncomp_value);
     };

     co_format_sack3_list_item = discriminator,
                                 block_1,
                                 block_2,
                                 block_3,
     {
       let(length:uncomp_value == 26);
       discriminator ::= '00000011';
       block_1 ::= tcp_opt_sack_block (ack_value);
       block_2 ::= tcp_opt_sack_block (block_1_end:uncomp_value);
       block_3 ::= tcp_opt_sack_block (block_2_end:uncomp_value);
     };

     co_format_sack4_list_item = discriminator,
                                 block_1,
                                 block_2,
                                 block_3,
                                 block_4,
     {
       let(length:uncomp_value == 34);
       discriminator ::= '00000100';
       block_1 ::= tcp_opt_sack_block (ack_value);
       block_2 ::= tcp_opt_sack_block (block_1_end:uncomp_value);
       block_3 ::= tcp_opt_sack_block (block_2_end:uncomp_value);
       block_4 ::= tcp_opt_sack_block (block_3_end:uncomp_value);
     };

     co_format_sack_unchanged_irregular = discriminator,
                                          block_1,
                                          block_2,
                                          block_3,
                                          block_4,
     {
       discriminator ::= '00000000';



Pelletier, et. al                                              [Page 69]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       block_1 ::= static;
       block_2 ::= static;
       block_3 ::= static;
       block_4 ::= static;
     };

     co_format_sack1_irregular = discriminator,
                                 block_1,
     {
       let(length:uncomp_value == 10);
       discriminator ::= '00000001';
       block_1 ::= tcp_opt_sack_block (ack_value);
     };

     co_format_sack2_irregular = discriminator,
                                 block_1,
                                 block_2,
     {
       let(length:uncomp_value == 18);
       discriminator ::= '00000010';
       block_1 ::= tcp_opt_sack_block (ack_value);
       block_2 ::= tcp_opt_sack_block (block_1_end:uncomp_value);
     };

     co_format_sack3_irregular = discriminator,
                                 block_1,
                                 block_2,
                                 block_3,
     {
       let(length:uncomp_value == 26);
       discriminator ::= '00000011';
       block_1 ::= tcp_opt_sack_block (ack_value);
       block_2 ::= tcp_opt_sack_block (block_1_end:uncomp_value);
       block_3 ::= tcp_opt_sack_block (block_2_end:uncomp_value);
     };

     co_format_sack4_irregular = discriminator,
                                 block_1,
                                 block_2,
                                 block_3,
                                 block_4,
     {
       let(length:uncomp_value == 34);
       discriminator ::= '00000100';
       block_1 ::= tcp_opt_sack_block (ack_value);
       block_2 ::= tcp_opt_sack_block (block_1_end:uncomp_value);
       block_3 ::= tcp_opt_sack_block (block_2_end:uncomp_value);
       block_4 ::= tcp_opt_sack_block (block_3_end:uncomp_value);
     };

   };



Pelletier, et. al                                              [Page 70]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   tcp_opt_sack_permitted ===
   {
     uc_format = type,   %[ 8 ]
                 length; %[ 8 ]

     default_methods =
     {
       type   ::= uncompressed_value (8, 4);
       length ::= uncompressed_value (8, 2);
     };
     co_format_sack_permitted_list_item =
     {
     };

     co_format_sack_permitted_irregular =
     {
     };

   };

   tcp_opt_generic ===
   {
     uc_format = type,       %[ 8 ]
                 length_msb, %[ 1 ]
                 length_lsb, %[ 7 ]
                 contents;   % n bits

     control_fields = option_static; %[ 1 ]

     default_methods =
     {
       type      ::= static;
       % lengths are always < 128
       % (i.e. the msb is always 0)
       length_msb    ::= uncompressed_value (1, 0);
       length_lsb    ::= static;
       contents      ::= static;
       let (option_static:uncomp_length == 1);
     };

     co_format_generic_list_item = type,          %[ 8 ]
                                   option_static, %[ 1 ]
                                   length_lsb,    %[ 7 ]
                                   contents,      % n bits
     {
       type          ::= irregular (8);
       option_static ::= irregular (1);
       length_lsb    ::= irregular (7);
       contents  ::= irregular (length_len:uncomp_value * 8 - 16);
     };




Pelletier, et. al                                              [Page 71]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     % Used when context of option has option_static set to one
     co_format_generic_irregular_static =
     {
       let(option_static:uncomp_value == 1);
     };

     % An item that can change, but currently is unchanged
     co_format_generic_irregular_stable = discriminator, %[ 8 ]
     {
       let(option_static:uncomp_value == 0);
       discriminator ::= '11111111';
     };

     % An item that can change, and has changed compared to context.
     % Length is not allowed to change here, since a length change is
     % most likely to cause new NOPs or an EOL length change.
     co_format_generic_irregular_full = discriminator, %[ 8 ]
                                        contents,      % n bits
     {
       let(option_static:uncomp_value == 0);
       discriminator ::= '00000000';
       contents      ::= irregular (length_lsb:uncomp_value * 8 - 16);
     };
   };

   list_tcp_options(nbits, ack_value) ===
   {
     uc_format = item,
                 tail;

     default_methods = {
     let(nbits >= item:uncomp_length);
     tail ::= list_tcp_options(nbits - item:uncomp_length, ack_value);
   };

     co_format_list_end =
     {
       let(nbits == 0);
       item ::= irregular(0);
       tail ::= irregular(0);
     };

     co_format_eol = item,
                     tail
     {
       let(nbits == item:uncomp_length); % redundant
       item ::= tcp_opt_eol(nbits);
       tail ::= irregular(0);
     };





Pelletier, et. al                                              [Page 72]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     co_format_nop = item,
                     tail
     {
       item ::= tcp_opt_nop;
     };

     co_format_mss  = item,
                      tail
     {
       item ::= tcp_opt_mss;
     };

     co_format_wscale = item,
                        tail
     {
       item ::= tcp_opt_wscale;
     };

     co_format_tsopt = item,
                       tail
     {
       item ::= tcp_opt_tsopt;
     };

     co_format_sack = item,
                      tail
     {
       item ::= tcp_opt_sack(ack_value);
     };

     co_format_permitted = item,
                           tail
     {
       item ::= tcp_opt_sack_permitted;
     };

     co_format_generic = item,
                         tail
     {
       item ::= tcp_opt_generic;
     };
   };

   tcp_list_presence_enc(list_length, presence, ack_value) ===
   {
     uc_format = tcp_options;

     co_format_list_not_present = tcp_options, %[ 0 ]
     {
       let (presence == 0);
       tcp_options ::= static;



Pelletier, et. al                                              [Page 73]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     };

     co_format_list_present = tcp_options, % 8 + n*8 bits
     {
       let (presence == 1);
       tcp_options ::= list_tcp_options(list_length, ack_value);
     };
   };


8.8.  Structures used in Compressed Base Headers

   tos_tc_enc(flag) ===
   {
     uc_format = tos_tc; %[ 6 ]

     co_format_static = tos_tc, %[ 0 ]
     {
       let (flag == 0);
       tos_tc             ::= static;
     };

     co_format_irreg = tos_tc,  %[ 6 ]
                       padding, %[ 2 ]
     {
       let (flag == 1);
       tos_tc             ::= irregular(6);
       padding            ::= compressed_value (2, 0);
     };
   };

   ip_id_lsb (behavior, k, p) ===
   {
     uc_format = ip_id; %[ 16 ]

     default_methods =
     {
       let (ip_id:uncomp_length == 16);
     };

     co_format_nbo = ip_id_offset, % k bits
     {
       let (behavior == 0);
       let (ip_id_offset:uncomp_value ==
            ip_id:uncomp_value - msn:uncomp_value);
       let (ip_id_offset:uncomp_length == 16);

       ip_id_offset ::= lsb (k, p);
     };





Pelletier, et. al                                              [Page 74]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     co_format_non_nbo = ip_id_offset, % k bits
     {
       let (behavior == 1);
       let (ip_id_nbo:uncomp_value == (ip_id:uncomp_value / 256) +
                                      (ip_id:uncomp_value & 255) * 256);
       let (ip_id_nbo:uncomp_length == 16);
       let (ip_id_offset:uncomp_value ==
            ip_id_nbo:uncomp_value - msn:uncomp_value);
       let (ip_id_offset:uncomp_length == 16);
       ip_id_offset ::= lsb (k, p);
     };
   };

   dont_fragment(version) ===
   {
     uc_format = df; %[ 1 ]

     co_format_v4 = df, %[ 1 ]
     {
       let (version == 4);
       df ::= irregular(1);
     };

     co_format_v6 = df,
     {
       let (version == 6);
       df ::= compressed_value(1,0);
     };
   };

   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   % Actual start of compressed packet formats
   % Important note: The base header is the
   % compressed representation of the innermost
   % IP header AND the TCP header.
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

   % ttl_irregular_chain_flag is an
   % "output argument" that should be passed
   % to the processing of the irregular chain
   % for outer IP headers.

   co_baseheader(payload_size, ttl_irregular_chain_flag) ===
   {
     uc_format_v4 = version,        %[  4 ]
                    header_length,  %[  4 ]
                    tos_tc,         %[  6 ]
                    ip_ecn_flags,   %[  2 ]
                    length,         %[ 16 ]
                    ip_id,          %[ 16 ]
                    rf,             %[  1 ]



Pelletier, et. al                                              [Page 75]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


                    df,             %[  1 ]
                    mf,             %[  1 ]
                    frag_offset,    %[ 13 ]
                    ttl_hopl,       %[  8 ]
                    next_header,    %[  8 ]
                    checksum,       %[ 16 ]
                    src_addr,       %[ 32 ]
                    dest_addr,      %[ 32 ]
                    src_port,       %[ 16 ]
                    dest_port,      %[ 16 ]
                    seq_number,     %[ 32 ]
                    ack_number,     %[ 32 ]
                    data_offset,    %[  4 ]
                    tcp_res_flags,  %[  4 ]
                    tcp_ecn_flags,  %[  2 ]
                    urg_flag,       %[  1 ]
                    ack_flag,       %[  1 ]
                    psh_flag,       %[  1 ]
                    rsf_flags,      %[  3 ]
                    window,         %[ 16 ]
                    tcp_checksum,   %[ 16 ]
                    urg_ptr,        %[ 16 ]
                    options_list,   % n bits
     {
       let (version:uncomp_value == 4);
     };

     uc_format_v6 = version,        %[   4 ]
                    tos_tc,         %[   6 ]
                    ip_ecn_flags,   %[   2 ]
                    flow_label,     %[  20 ]
                    payload_length, %[  16 ]
                    next_header,    %[   8 ]
                    ttl_hopl,       %[   8 ]
                    src_addr,       %[ 128 ]
                    dest_addr,      %[ 128 ]
                    src_port,       %[  16 ]
                    dest_port,      %[  16 ]
                    seq_number,     %[  32 ]
                    ack_number,     %[  32 ]
                    data_offset,    %[   4 ]
                    tcp_res_flags,  %[   4 ]
                    tcp_ecn_flags,  %[   2 ]
                    urg_flag,       %[   1 ]
                    ack_flag,       %[   1 ]
                    psh_flag,       %[   1 ]
                    rsf_flags,      %[   3 ]
                    window,         %[  16 ]
                    tcp_checksum,   %[  16 ]
                    urg_ptr,        %[  16 ]
                    options_list,   % n bits



Pelletier, et. al                                              [Page 76]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     {
       let (version:uncomp_value == 6);
     };

     control_fields  = ip_id_behavior;   % 2 bits

     default_methods =
     {
       version           ::= static;
       tos_tc            ::= static;
       ip_ecn_flags      ::= static;
       ttl_hopl          ::= static;
       next_header       ::= static;
       src_addr          ::= static;
       dest_addr         ::= static;
       flow_label        ::= static;
       payload_length    ::= inferred_ip_v6_length;
       header_length     ::= uncompressed_value (4,5);
       length            ::= inferred_ip_v4_length;
       ip_id             ::= irregular(16);
       ip_id_behavior    ::= static;
       rf                ::= static;
       df                ::= static;
       mf                ::= static;
       frag_offset       ::= static;
       checksum          ::= inferred_ip_v4_header_checksum;
       src_port          ::= static;
       dest_port         ::= static;
       seq_number        ::= static;
       ack_number        ::= static;
       data_offset       ::= inferred_offset;
       tcp_ecn_flags     ::= static;
       psh_flag          ::= irregular (1);
       urg_flag          ::= uncompressed_value (1, 0);
       ack_flag          ::= uncompressed_value (1, 1);
       window            ::= static;
       tcp_checksum      ::= irregular(16);
       urg_ptr           ::= static;
       rsf_flags         ::= uncompressed_value (3, 0);
       tcp_res_flags     ::= static;
       options_list      ::= static;

       let (version:uncomp_length == 4);
       let (seq_number_scaled:uncomp_value ==
            seq_number:uncomp_value / payload_size);
       let (seq_number_residue:uncomp_value ==
            mod(seq_number:uncomp_value, payload_size));
       let (ack_number:uncomp_value ==
                                     (ack_stride:uncomp_value *
                                      ack_number_scaled:uncomp_value) +
                                      ack_number_residue:uncomp_value);



Pelletier, et. al                                              [Page 77]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       let (ack_number_residue:uncomp_value ==
                 mod(ack_number:uncomp_value, ack_stride:uncomp_value));
     };

   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   % Common compressed packet format
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

     co_format_co_common = discriminator,        %[ 7 ]
                           ttl_hopl_outer_flag,  %[ 1 ]
                           ack_flag,             %[ 1 ]
                           psh_flag,             %[ 1 ]
                           rsf_flags,            %[ 2 ]
                           msn,                  %[ 4 ]
                           seq_indicator,        %[ 2 ]
                           ack_indicator,        %[ 2 ]
                           ack_stride_indicator, %[ 1 ]
                           window_indicator,     %[ 1 ]
                           ip_id_indicator,      %[ 2 ]
                           urg_ptr_present,      %[ 1 ]
                           ecn_used,             %[ 1 ]
                           tos_tc_present,       %[ 1 ]
                           ttl_hopl_present,     %[ 1 ]
                           list_present,         %[ 1 ]
                           ip_id_behavior,       %[ 2 ]
                           urg_flag,             %[ 1 ]
                           df,                   %[ 1 ]
                           header_crc,           %[ 7 ]
                           seq_number,           % 0, 8, 16, 32 bits
                           ack_number,           % 0, 8, 16, 32 bits
                           ack_stride,           % 0 or 16 bits
                           window,               % 0 or 16 bits
                           ip_id,                % 0, 8, 16 bits
                           urg_ptr,              % 0 or 16 bits
                           tos_tc,               % 0 or 8 bits
                           ttl_hopl,             % 0 or 8 bits
                           options_list,         % n bits
     {
       discriminator      ::= '1111101';
       ttl_hopl_outer_flag::= irregular(1);
       % Need to bind argument so that it can be passed to the
       % structure for IPv4/IPv6 irregular chain.
       let(ttl_irregular_chain_flag ==
                                      ttl_hopl_outer_flag:uncomp_value);
       tos_tc_present   ::= irregular(1);
       ttl_hopl_present ::= irregular(1);
       ack_flag         ::= irregular(1);
       psh_flag         ::= irregular(1);
       msn              ::= lsb (4, 3);
       df               ::= dont_fragment(version:uncomp_value);
       header_crc       ::= crc7(this:uncomp_value, this:uncomp_length);



Pelletier, et. al                                              [Page 78]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       urg_flag         ::= irregular(1);
       urg_ptr_present  ::= irregular(1);
       ecn_used         ::= irregular(1);
       list_present     ::= irregular(1);
       ip_id_behavior   ::= ip_id_behavior_enc;
       rsf_flags        ::= rsf_index_enc;
       window_indicator ::= irregular(1);
       ip_id_indicator  ::= irregular(2);
       seq_indicator    ::= irregular(2);
       ack_indicator    ::= irregular(2);

       ack_stride_indicator ::= irregular(1);

       seq_number ::= variable_length_32_enc(seq_indicator:comp_value);
       ack_number ::= variable_length_32_enc(ack_indicator:comp_value);

       ack_stride   ::=
                    static_or_irreg16(ack_stride_indicator:comp_value);

       window    ::= static_or_irreg16(window_indicator:comp_value);
       ip_id     ::= variable_length_16_enc(ip_id_indicator:comp_value);

       urg_ptr        ::= static_or_irreg16(urg_ptr_present:comp_value);
       ttl_hopl       ::= static_or_irreg8(ttl_hopl_present:comp_value);
       tos_tc         ::= tos_tc_enc(tos_tc_present:comp_value);
       options_list   ::= tcp_list_presence_enc
                          ((data_offset:uncomp_value - 5) * 32,
                            list_present:comp_value,
                            ack_number:uncomp_value);
   };

   % NON-SEQUENTIAL PACKET FORMATS
   % +------+--------+-----+-----+-----+---------+---------+
   % |Name  |Disc    |MSN  |SN   |ACK  |Window   |Comment  |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_1    |10111110|4    |16   |0    |         |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_2    |1100    |4    |*4   |0    |         |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_3    |0       |4    |0    |15   |         |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_4    |1101    |4    |0    |4*   |         |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_5    |100     |4    |14   |15   |         |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_6    |10110   |4    |*4   |15   |         |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_7    |1010    |4    |14   |0    |14       |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_8    |10111111|4    |0    |16   |16       |         |
   % +------+--------+-----+-----+-----+---------+---------+



Pelletier, et. al                                              [Page 79]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   % |_9    |101110  |4    |*4   |0    |14       |         |
   % +------+--------+-----+-----+-----+---------+---------+
   % |_10   |1011110 |4    |14   |16   |         |and more |
   % +------+--------+-----+-----+-----+---------+---------+

     % Send LSBs of sequence number

     co_format_rnd_1 = discriminator, %[ 8 ]
                       seq_number,    %[ 16 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '10111110';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       seq_number          ::= lsb(16, 32767);
     };

     % Send scaled sequence number LSBs
     co_format_rnd_2 = discriminator,     %[ 4 ]
                       seq_number_scaled, %[ 4 ]
                       msn,               %[ 4 ]
                       psh_flag,          %[ 1 ]
                       header_crc,        %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '1100';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       seq_number_scaled   ::= lsb(4, 7);
       seq_number_residue  ::= static;
     };

     % Send acknowledgement number LSBs
     co_format_rnd_3 = discriminator, %[ 1 ]
                       ack_number,    %[ 15 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '0';



Pelletier, et. al                                              [Page 80]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       ack_number          ::= lsb(15, 8191);
     };

     % Send acknowledgement number scaled
     co_format_rnd_4 = discriminator,     %[ 4 ]
                       ack_number_scaled, %[ 4 ]
                       msn,               %[ 4 ]
                       psh_flag,          %[ 1 ]
                       header_crc,        %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '1101';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       ack_number_scaled   ::= lsb(4, 3);
       ack_number_residue  ::= static;
     };

     % Send ACK and sequence number
     co_format_rnd_5 = discriminator, %[ 3 ]
                       psh_flag,      %[ 1 ]
                       msn,           %[ 4 ]
                       header_crc,    %[ 3 ]
                       seq_number,    %[ 14 ]
                       ack_number,    %[ 15 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '100';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       ack_number          ::= lsb(15, 8191);
       seq_number          ::= lsb(14, 8191);
     };

     % Send both ACK and scaled sequence number LSBs
     co_format_rnd_6 = discriminator,     %[ 5 ]
                       header_crc,        %[ 3 ]
                       psh_flag,          %[ 1 ]
                       ack_number,        %[ 15 ]
                       msn,               %[ 4 ]
                       seq_number_scaled, %[ 4 ],



Pelletier, et. al                                              [Page 81]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '10110';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       ack_number          ::= lsb(15, 8191);
       seq_number_scaled   ::= lsb(4, 7);
       seq_number_residue  ::= static;
     };

     % Send sequence number and window
     co_format_rnd_7 = discriminator, %[ 4 ]
                       seq_number,    %[ 14 ]
                       window,        %[ 14 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '1010';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       seq_number          ::= lsb(14, 8191);
       window              ::= lsb(14, 8191);
     };

     % Send ACK and window
     co_format_rnd_8 = discriminator, %[ 8 ]
                       ack_number,    %[ 16 ]
                       window,        %[ 16 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '10111111';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       ack_number          ::= lsb(16, 16383);
       window              ::= irregular(16);
     };




Pelletier, et. al                                              [Page 82]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     % Send scaled sequence number and window.
     co_format_rnd_9 = discriminator,     %[ 6 ]
                       seq_number_scaled, %[ 4 ]
                       window,            %[ 14 ]
                       msn,               %[ 4 ]
                       psh_flag,          %[ 1 ]
                       header_crc,        %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '101110';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc3 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       window              ::= lsb(14, 8191);
       seq_number_scaled   ::= lsb(4, 3);
       seq_number_residue  ::= static;
     };

     % A packet halfway between co_common and compressed packets
     % Can send LSBs of TTL, RSF flags,
     % change ECN behavior and options list
     co_format_rnd_10 = discriminator, %[ 7 ]
                        ecn_used,      %[ 1 ]
                        list_present,  %[ 1 ]
                        header_crc,    %[ 7 ]
                        msn,           %[ 4 ]
                        psh_flag,      %[ 1 ]
                        ttl_hopl,      %[ 3 ]
                        rsf_flags,     %[ 2 ]
                        seq_number,    %[ 14 ]
                        ack_number,    %[ 16 ]
                        options_list,  % 0 or X bits
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '1011110';
       msn                 ::= lsb(4, 4);
       header_crc          ::= crc7 (this:uncomp_value,
                                     this:uncomp_length);
       psh_flag            ::= irregular (1);
       list_present        ::= irregular(1);
       options_list        ::= tcp_list_presence_enc
                              ((data_offset:uncomp_value - 5) * 32,
                                list_present:comp_value,
                                ack_number:uncomp_value);
       rsf_flags           ::= rsf_index_enc;
       ecn_used            ::= irregular(1);
       ttl_hopl            ::= lsb(3, 3);
       seq_number          ::= lsb(14, 8191);



Pelletier, et. al                                              [Page 83]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       ack_number          ::= lsb(16, 16383);
     };


   % SEQUENTIAL PACKET FORMATS
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |Name  |Disc  |MSN  |ID   |SN   |ACK  |Win  |Comment  |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_1    |1010  |4    |4    |16   |0    |     |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_2    |11001 |4    |7    |*4   |0    |     |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_3    |1001  |4    |4    |0    |16   |     |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_4    |0     |4    |3    |0    |*4   |     |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_5    |1000  |4    |4    |16   |16   |     |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_6    |110110|4    |6    |*4   |16   |     |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_7    |11010 |4    |5    |14   |0    |16   |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_8    |11000 |4    |5    |0    |16   |14   |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_9    |110111|4    |6    |*4   |0    |16   |         |
   % +------+------+-----+-----+-----+-----+-----+---------+
   % |_10   |1011  |4    |4    |14   |15   |     |and more |
   % +------+------+-----+-----+-----+-----+-----+---------+

     % Send LSBs of sequence number
     co_format_seq_1 = discriminator, %[ 4 ]
                       ip_id,         %[ 4 ]
                       seq_number,    %[ 16 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator  ::= '1010';
       msn            ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 4, 3);
       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag       ::= irregular (1);
       seq_number     ::= lsb(16, 32767);
     };

     % Send scaled sequence number LSBs
     co_format_seq_2 = discriminator,     %[ 5 ]
                       ip_id,             %[ 7 ]



Pelletier, et. al                                              [Page 84]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


                       seq_number_scaled, %[ 4 ]
                       msn,               %[ 4 ]
                       psh_flag,          %[ 1 ]
                       header_crc,        %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator  ::= '11001';
       msn            ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 7, 3);
         header_crc   ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag            ::= irregular (1);
       seq_number_scaled   ::= lsb(4, 7);
       seq_number_residue  ::= static;
     };

     % Send acknowledgement number LSBs
     co_format_seq_3 = discriminator, %[ 4 ]
                       ip_id,         %[ 4 ]
                       ack_number,    %[ 16 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator  ::= '1001';
       msn            ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 4, 3);
       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag       ::= irregular (1);
       ack_number     ::= lsb(16, 16383);
     };

     % Send scaled acknowledgement number scaled
     co_format_seq_4 = discriminator,     %[ 1 ]
                       ack_number_scaled, %[ 4 ]
                       ip_id,             %[ 3 ]
                       msn,               %[ 4 ]
                       psh_flag,          %[ 1 ]
                       header_crc,        %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator  ::= '0';
       msn            ::= lsb(4, 4);
       % Note that due to having very few ip_id bits,
       % no reordering offset
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 3, 1);



Pelletier, et. al                                              [Page 85]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag            ::= irregular (1);
       ack_number_scaled   ::= lsb(4, 3);
       ack_number_residue  ::= static;
     };

     % Send ACK and sequence number
     co_format_seq_5 = discriminator, %[ 4 ]
                       ip_id,         %[ 4 ]
                       ack_number,    %[ 16 ]
                       seq_number,    %[ 16 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator  ::= '1000';
       msn            ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 4, 3);
       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag            ::= irregular (1);
       ack_number          ::= lsb(16, 16383);
       seq_number          ::= lsb(16, 32767);
     };

     % Send both ACK and scaled sequence number LSBs
     co_format_seq_6 = discriminator,     %[ 6 ]
                       seq_number_scaled, %[ 4 ]
                       ip_id,             %[ 6 ]
                       ack_number,        %[ 16 ]
                       msn,               %[ 4 ]
                       psh_flag,          %[ 1 ]
                       header_crc,        %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '110110';
       seq_number_scaled   ::= lsb(4, 7);
       seq_number_residue  ::= static;
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 6, 3);
       ack_number     ::= lsb(16, 16383);
       msn            ::= lsb(4, 4);
       psh_flag       ::= irregular (1);
       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
     };





Pelletier, et. al                                              [Page 86]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


     % Send sequence number and window
     co_format_seq_7 = discriminator, %[ 5 ]
                       seq_number,    %[ 14 ]
                       ip_id,         %[ 5 ]
                       window,        %[ 16 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '11010';
       msn                 ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 5, 3);
       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag       ::= irregular (1);
       seq_number     ::= lsb(14, 8191);
       window         ::= irregular(16);
     };

     % Send ACK and window
     co_format_seq_8 = discriminator, %[ 5 ]
                       window,        %[ 14 ]
                       ip_id,         %[ 5 ]
                       ack_number,    %[ 16 ]
                       msn,           %[ 4 ]
                       psh_flag,      %[ 1 ]
                       header_crc,    %[ 3 ]
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '11000';
       msn                 ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 5, 3);
       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag       ::= irregular (1);
       ack_number     ::= lsb(16, 32767);
       window         ::= lsb(14, 8191);
     };

     % Send scaled sequence number and window.
     co_format_seq_9 = discriminator,     %[ 6 ]
                       ip_id,             %[ 6 ]
                       seq_number_scaled, %[ 4 ]
                       window,            %[ 16 ]
                       msn,               %[ 4 ]
                       psh_flag,          %[ 1 ]
                       header_crc,        %[ 3 ]
     {



Pelletier, et. al                                              [Page 87]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '110111';
       msn                 ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 6, 3);
       header_crc     ::= crc3 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag       ::= irregular (1);
       window         ::= irregular(16);
       seq_number_scaled   ::= lsb(4, 7);
       seq_number_residue  ::= static;
     };

     % A packet halfway between co_common and compressed packets
     % Can send LSBs of TTL, RSF flags,
     % change ECN behavior and options list
     co_format_seq_10 = discriminator, %[ 4 ]
                        ip_id,         %[ 4 ]
                        list_present,  %[ 1 ]
                        header_crc,    %[ 7 ]
                        msn,           %[ 4 ]
                        psh_flag,      %[ 1 ]
                        ttl_hopl,      %[ 3 ]
                        ecn_used,      %[ 1 ]
                        ack_number,    %[ 15 ]
                        rsf_flags,     %[ 2 ]
                        seq_number,    %[ 14 ]
                        options_list,  % Nx8 bits
     {
       let ((ip_id_behavior:uncomp_value == 2) ||
            (ip_id_behavior:uncomp_value == 3));
       discriminator       ::= '1011';
       msn                 ::= lsb(4, 4);
       ip_id          ::= ip_id_lsb (ip_id_behavior:uncomp_value, 4, 3);
       header_crc     ::= crc7 (this:uncomp_value,
                                this:uncomp_length);
       psh_flag       ::= irregular (1);
       list_present   ::= irregular(1);
       options_list   ::= tcp_list_presence_enc
                          ((data_offset:uncomp_value - 5) * 32,
                           list_present:comp_value);
       rsf_flags      ::= rsf_index_enc;
       ecn_used       ::= irregular(1);
       ttl_hopl       ::= lsb(3, 3);
       seq_number     ::= lsb(14, 8191);
       ack_number     ::= lsb(15, 8191);
     };
   };






Pelletier, et. al                                              [Page 88]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.9. Feedback Formats and Options


8.9.1. Feedback Formats

   This section describes the feedback format for ROHC-TCP. ROHC-TCP
   uses the ROHC feedback format described in section 5.2.2 of [2].

   All feedback formats carry a field labeled SN. The SN field contains
   LSBs of the Master Sequence Number (MSN) described in section 6.3.1.
   The sequence number to use is the MSN corresponding to the header
   that caused the feedback information to be sent. If that MSN cannot
   be determined, for example when decompression fails, the MSN to use
   is that corresponding to the latest successfully decompressed header.

   FEEDBACK-1

     0   1   2   3   4   5   6   7
   +---+---+---+---+---+---+---+---+
   |              MSN              |
   +---+---+---+---+---+---+---+---+

      MSN: The lsb-encoded master sequence number.

   A FEEDBACK-1 is an ACK.  In order to send a NACK or a STATIC-NACK,
   FEEDBACK-2 must be used.

   FEEDBACK-2

     0   1   2   3   4   5   6   7
   +---+---+---+---+---+---+---+---+
   |Acktype|         MSN           |
   +---+---+---+---+---+---+---+---+
   |              MSN              |
   +---+---+---+---+---+---+---+---+
   /       Feedback options        /
   +---+---+---+---+---+---+---+---+

      Acktype:  0 = ACK
                1 = NACK
                2 = STATIC-NACK
                3 is reserved (MUST NOT be used for parseability)

      MSN: The lsb-encoded master sequence number.


      Feedback options: A variable number of feedback options, see
                       section 8.9.2. Options may appear in any order.






Pelletier, et. al                                              [Page 89]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.9.2. Feedback Options

   A ROHC-TCP Feedback option has variable length and the following
   general format:

     0   1   2   3   4   5   6   7
   +---+---+---+---+---+---+---+---+
   |   Opt Type    |    Opt Len    |
   +---+---+---+---+---+---+---+---+
   /          option data          /  Opt Len octets
   +---+---+---+---+---+---+---+---+


8.9.2.1. The CRC option

   The CRC option contains an 8-bit CRC computed over the entire
   feedback payload, without the packet type and code octet, but
   including any CID fields, using the polynomial of section 5.9.1 of
   [2].  If the CID is given with an Add-CID octet, the Add-CID octet
   immediately precedes the FEEDBACK-1 or FEEDBACK-2 format.  For
   purposes of computing the CRC, the CRC fields of all CRC options are
   zero.

     0   1   2   3   4   5   6   7
   +---+---+---+---+---+---+---+---+
   |  Opt Type = 1 |  Opt Len = 1  |
   +---+---+---+---+---+---+---+---+
   |              CRC              |
   +---+---+---+---+---+---+---+---+

   When receiving feedback information with a CRC option, the compressor
   MUST verify the information by computing the CRC and comparing the
   result with the CRC carried in the CRC option.  If the two are not
   identical, the feedback information MUST be ignored.


8.9.2.2. The REJECT option

   The REJECT option informs the compressor that the decompressor does
   not have sufficient resources to handle the flow.

   +---+---+---+---+---+---+---+---+
   |  Opt Type = 2 |  Opt Len = 0  |
   +---+---+---+---+---+---+---+---+

   When receiving a REJECT option, the compressor stops compressing the
   packet stream, and should refrain from attempting to increase the
   number of compressed packet streams for some time.  Any FEEDBACK
   packet carrying a REJECT option MUST also carry a CRC option.





Pelletier, et. al                                              [Page 90]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.9.2.3. The MSN-NOT-VALID option

   The MSN-NOT-VALID option indicates that the MSN of the feedback is
   not valid.  A compressor MUST NOT use the MSN of the feedback to find
   the corresponding sent header when this option is present.

   +---+---+---+---+---+---+---+---+
   |  Opt Type = 3 |  Opt Len = 0  |
   +---+---+---+---+---+---+---+---+


8.9.2.4. The MSN option

   The MSN option provides 8 additional bits of MSN.

   +---+---+---+---+---+---+---+---+
   |  Opt Type = 4 |  Opt Len = 1  |
   +---+---+---+---+---+---+---+---+
   |              MSN              |
   +---+---+---+---+---+---+---+---+


8.9.2.5. The LOSS option

   The LOSS option allows the decompressor to report the largest
   observed number of packets lost in sequence.

   +---+---+---+---+---+---+---+---+
   |  Opt Type = 7 |  Opt Len = 1  |
   +---+---+---+---+---+---+---+---+
   | longest loss event (packets)  |
   +---+---+---+---+---+---+---+---+

   The decompressor MAY choose to ignore the oldest loss events.  Thus,
   the value reported may decrease.  Since setting the reference window
   too small can reduce robustness, a FEEDBACK packet carrying a LOSS
   option SHOULD also carry a CRC option.  The compressor MAY choose to
   ignore decreasing loss values.


8.9.2.6. Unknown option types

   If an option type unknown to the compressor is encountered, it must
   continue parsing the rest of the FEEDBACK packet, which is possible
   since the length of the option is explicit, but MUST otherwise ignore
   the unknown option.








Pelletier, et. al                                              [Page 91]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


8.9.2.7. The CONTEXT_MEMORY Feedback Option

   The CONTEXT_MEMORY option informs the compressor that the
   decompressor does not have sufficient memory resources to handle the
   context of the packet stream, as the stream is currently compressed.

     0   1   2   3   4   5   6   7
   +---+---+---+---+---+---+---+---+
   |  Opt Type = 9 |  Opt Len = 0  |
   +---+---+---+---+---+---+---+---+

   When receiving a CONTEXT_MEMORY option, the compressor SHOULD take
   actions to compress the packet stream in a way that requires less
   decompressor memory resources, or stop compressing the packet stream.


9. Security Consideration

   Because encryption eliminates the redundancy that header compression
   schemes try to exploit, there is some inducement to forego encryption
   of headers in order to enable operation over low-bandwidth links.
   However, for those cases where encryption of data (and not headers)
   is sufficient, TCP does specify an alternative encryption method in
   which only the TCP payload is encrypted and the headers are left in
   the clear.  That would still allow header compression to be applied.

   A malfunctioning or malicious header compressor could cause the
   header decompressor to reconstitute packets that do not match the
   original packets but still have valid IP, and TCP headers and
   possibly also valid TCP checksums.  Such corruption may be detected
   with end-to-end authentication and integrity mechanisms that will not
   be affected by the compression.  Moreover, this header compression
   scheme uses an internal checksum for verification of reconstructed
   headers.  This reduces the probability of producing decompressed
   headers not matching the original ones without this being noticed.

   Denial-of-service attacks are possible if an intruder can introduce
   (for example) bogus IR, CO or FEEDBACK packets onto the link and
   thereby cause compression efficiency to be reduced.  However, an
   intruder having the ability to inject arbitrary packets at the link
   layer in this manner raises additional security issues that dwarf
   those related to the use of header compression.












Pelletier, et. al                                              [Page 92]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


10. IANA Considerations

   The ROHC profile identifier 0x00XX <# Editor's Note: To be replaced
   before publication #> has been reserved by the IANA for the profile
   defined in this document.

   <# Editor's Note: To be removed before publication #>

   A ROHC profile identifier must be reserved by the IANA for the
   profile defined in this document.  Profiles 0x0000-0x0005 have
   previously been reserved, which means this profile could be 0x0006.
   As for previous ROHC profiles, profile numbers 0xnnXX must also be
   reserved for future updates of this profile.  A suggested
   registration in the "RObust Header Compression (ROHC) Profile
   Identifiers" name space would then be:

     Profile             Usage            Document
     identifier

     0x0006              ROHC TCP         [RFCXXXX (this)]
     0xnn06              Reserved


11. Acknowledgments

   The authors would like to thank Qian Zhang, Hong Bin Liao and Richard
   Price for their work with early versions of this specification.
   Thanks also to Fredrik Lindstroem for reviewing the packet formats,
   as well as to Robert Finking for valuable input.


12. Authors' Addresses

      Ghyslain Pelletier
      Ericsson AB
      Box 920
      SE-971 28 Lulea, Sweden

      Phone: +46 8 404 29 43
      Fax:   +46 920 996 21
      EMail: ghyslain.pelletier@ericsson.com


      Lars-Erik Jonsson
      Ericsson AB
      Box 920
      SE-971 28 Lulea, Sweden

      Phone: +46 8 404 29 61
      Fax:   +46 920 996 21
      EMail: lars-erik.jonsson@ericsson.com



Pelletier, et. al                                              [Page 93]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005




      Mark A West
      Roke Manor Research Ltd
      Romsey, Hants, SO51 0ZN
      United Kingdom

      Phone: +44 1794 833311
      Email: mark.a.west@roke.co.uk


      Carsten Bormann
      Universitaet Bremen TZI
      Postfach 330440
      Bremen  D-28334
      Germany

      Phone: +49 421 218 7024
      Fax:   +49 421 218 7000
      EMail: cabo@tzi.org


      Kristofer Sandlund
      Effnet AB
      Stationsgatan 69
      S-972 34 Lulea
      Sweden

      Phone:  +46 920 609 17
      Fax:    +46 920 609 27
      EMail:  kristofer.sandlund@effnet.com


13. References

13.1. Normative references

   [1]  S. Bradner, "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, March 1997.

   [2]  Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
        Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le, K., Liu,
        Z., Martensson, A., Miyazaki, A., Svanbro, K., Wiebke, T.,
        Yoshimura, T. and H. Zheng, "RObust Header Compression (ROHC):
        Framework and four profiles: RTP, UDP, ESP, and uncompressed",
        RFC 3095, July 2001.

   [3]  Pelletier, G., "Robust Header Compression (ROHC): Context
        Replication for ROHC profiles", Internet Draft (work in
        progress), <draft-ietf-rohc-context-replication-06.txt>, October
        2004.



Pelletier, et. al                                              [Page 94]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   [4]  R. Finking, C. Bormann and G. Pelletier, "Formal Notation for
        Robust Header Compression (ROHC-FN)", Internet Draft (work in
        progress), <draft-ietf-rohc-formal-notation-04.txt>, February
        2005.

   [5]  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.

   [6]  Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
        September 1981.

   [7]  S. Bradner, "The Internet Standards Process - Revision 3", RFC
        2026, October 1996.

   [8]  S. Bradner, "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, March 1997.

   [9]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
        Specification", RFC 2460, December 1998.



13.2. Informative References

   [10] Jonsson, L-E., "Requirements on ROHC IP/TCP header compression",
        Internet Draft (work in progress), <draft-ietf-rohc-tcp-
        requirements-08.txt>, September 2004.

   [11] West, M. and S. McCann, "TCP/IP Field Behavior", Internet Draft
        (work in progress), <draft-ietf-rohc-tcp-field-behavior-04.txt>,
        October 2004.

   [12] Jonsson, L-E. and G. Pelletier, "RObust Header Compression
        (ROHC): A compression profile for IP", RFC 3843, June 2003.

   [13] Jacobson, V., and R. Braden, "TCP Extensions for Long-Delay
        Paths", LBL, ISI, October 1988.

   [14] Jacobson, V.,"Compressing TCP/IP Headers for Low-Speed Serial
        Links", RFC 1144, February 1990.

   [15] Jacobson, V., Braden, R. and D. Borman, "TCP Extensions for High
        Performance", RFC 1323, May 1992.

   [16] Braden, R. "T/TCP -- TCP Extensions for Transactions Functional
        Specification", ISI, July 1994.

   [17] Connolly, T., et al, "An Extension to TCP: Partial Order
        Service", University of Delaware, November 1994.






Pelletier, et. al                                              [Page 95]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


   [18] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications", RFC
        1889, January 1996.

   [19] Stevens, W., "TCP Slow Start, Congestion Avoidance, Fast
        Retransmit, and Fast Recovery Algorithms", NOAO, January 1997.

   [20] Mathis, M., Mahdavi, J., Floyd, S. and A. Romanow, "TCP
        Selective Acknowledgment Options", RFC 2018, October 1996.

   [21] Degermark, M., Nordgren, B. and S. Pink, "IP Header
        Compression", RFC 2507, February 1999.

   [22] Floyd, S., Mahdavi, J., Mathis, M. and M. Podolsky, "An
        Extension to the Selective Acknowledgement (SACK) Option for
        TCP", RFC 2883, July 2000.

   [23] Ramakrishnan, K., Floyd and D. Black, "The Addition of Explicit
        Congestion Notification (ECN) to IP", RFC 3168, September 2001.

   [24] Jacobson, V., "Fast Retransmit", Message to the end2end-interest
        mailing list, April 1990.

   [25] Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
        October 1996.





























Pelletier, et. al                                              [Page 96]

INTERNET-DRAFT           ROHC Profile for TCP/IP       February 21, 2005


Copyright Statement

   Copyright (C) The Internet Society (2004). This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


































This Internet-Draft expires August 21, 2005.



Pelletier, et. al                                              [Page 97]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/